Equilibrium Fluid Research Articles

Methane-bearing fluids in the upper mantle: an experimental approach

The main obstacle to understanding of the geological role of reduced, CH4-bearing fluids is the absence of a reliable experimental technique applicable to solid-media high-pressure apparatuses, allowing their observation and direct characterisation under laboratory conditions. In this study, we describe the main pitfalls of earlier designs and technical aspects related to achievement of strongly reduced oxygen fugacity (fO2) conditions (i.e., Fe–FeO, IW) and maintenance of a constant fluid equilibrium during an experiment. We describe a new triple-capsule design made of an Au outer capsule with an Au-inner capsule containing a metal/metal oxide oxygen buffer and water, as well as an inner olivine container filled with a harzburgitic sample material and Ir powder that serves as a redox sensor. The bottom of the outer capsule is covered with a solid fluid source (e.g., stearic acid). The outer capsule is surrounded by a polycrystalline CaF2 pressure medium to minimise H2-loss from the assembly. Application of this design is limited to temperatures below the melting temperature of Au, which is pressure dependent. Metals other than Au can lead to fluid disequilibrium triggered by a dehydrogenation and carbonation of the methane. Test experiments were carried out at 5 GPa, temperatures < 1300 °C, at Mo–MoO2 and Fe–FeO buffer conditions. IrFe alloy sensors demonstrate successful achievement and maintenance of reduced fluid environment at ∆logfO2 ≈ IW + 0.5. The fluid phase was trapped in numerous inclusions within the olivine sample container. Raman spectra reveal that the fluid consists mainly of CH4, along with small amounts of higher hydrocarbons like C2H6. No water was detected, but H2 was found to be present in fluid and incorporated into the olivine structure. Our results are inconsistent with published fluid speciation models that predict significant H2O contents at these fO2 conditions. It is also apparent that fluids with significant CH4 contents are likely to be stable under the conditions recorded by some mantle samples.

Geochemical Specifics of Highly Differentiated Topaz-Bearing Granite of the Salmi Batholith

Two varieties of highly differentiated topaz-bearing granite of the Salmi Batholith are distinguished: Li-siderophyllite topaz-bearing granite (Li-Sdph) (Lupikko dome) and Li–F-topaz-zinnwaldite granite (Li–F-Znwl) (Uksinskii dome). Their geochemical patterns and their place in the evolution of the compositions of A-type granite magma derivatives are shown using indicators of crystallization differentiation and the mineragenic potential; the likely regime of the volatile components (water activity in the melt and F accumulation) is discussed. The physicochemical conditions of the formation of Li–F granite were studied. The solidus temperature was determined experimentally by the method of rock powder melting (570–640°C under water saturated and dry conditions). Based on the temperatures of rock formation obtained and the data on the composition of micas, the F content in the fluid in equilibrium with micas (~0.24–0.34 mol/dm3 HF) was estimated. This similarity of the evolutionary trends for granite magmatism of the studied rocks and commercial Ta–Nb objects of Eastern Transbaikalia (S-type granite) is shown.

Galactic Constraints on Fermionic Dark Matter

In order to explain Galactic structures, a self-gravitating system composed of massive fermions in spherical symmetry is considered. The finite mass distribution of such a component is obtained after solving the Einstein equation for a thermal and semi-degenerate fermionic gas, described by a perfect fluid in hydrostatic equilibrium and exposed to cutoff effects (e.g. evaporation). Within this more general approach a family of density profiles arises, which explains dark matter halo constraints of the Galaxy and provides at the same time an alternative to the central black hole scenario in Sgr A*. This analysis narrows the allowed particle mass to mc2 = 48−345 keV.

Low temperature stable mineral recrystallization of foraminiferal tests and implications for the fidelity of geochemical proxies

Fossilized foraminiferal tests are widely used as proxies to constrain paleoenvironments, including past sea surface and bottom water temperatures and the chemical composition of ancient seawater. However, relatively little is known about the extent to which calcareous foraminiferal tests exchange with seawater prior to burial. In this study, we used a 45Ca radiotracer approach to quantify the extent and rate of foraminiferal calcite–fluid exchange over a three-month period. Modern foraminiferal tests exhibited faster exchange with a 45Ca-spiked solution (2.6⋅10−4 to 2.0⋅10−5 mol/m2/d) than fossil foraminiferal tests (7.6⋅10−5 to 5.3⋅10−6 mol/m2/d) from ODP Site 807. The impact of dissolved Si on the exchange rate of modern foraminifera was minimal (2.6⋅10−4 to 9.2⋅10−6 mol/m2/d). Unlike foraminiferal calcite, inorganic calcite exchanged at remarkably slow rates (6.6⋅10−6 to 5.9⋅10−7 mol/m2/d) suggesting that biogenic calcite is more reactive than inorganic calcite. Increased Ca2+, Mg2+, and Sr2+ concentrations in fluids from parallel tracer-free reactors indicated preferential dissolution of tests, though there was no overt change in test morphology during experiments (as imaged by scanning electron microscopy and micro-CT scanning). Time-dependent box model simulations of 45Ca, as well as aqueous elemental chemistry, support the hypothesis that calcite–fluid exchange occurred via dissolution–reprecipitation of foraminiferal tests that was induced by intra-test chemical heterogeneity. The short-term exchange reactions investigated in this study are comparable to the reactions that can occur in the seawater column and at the sediment–seawater interface. This work suggests that dissolution–reprecipitation in such settings has the potential to overprint the chemistry of foraminiferal tests without overt physical alteration, which can lead to a potential bias in paleoenvironmental reconstructions. Model-based estimates suggest a maximum of 2–3°C alteration of Mg/Ca-based temperatures over experimental time scales. Model efforts also suggest that the diagenetic trajectories in Mg/Ca–δ18O space, for instance, are impacted by the partition coefficient of Mg in calcite (λMg) as well as by the mechanism of alteration. This is demonstrated for (i) the ratio of exchange to dissolution and (ii) the relative rate of high-Mg-calcite to low-Mg-calcite reaction. We have illustrated that the mechanism of alteration, in addition to water-rock ratios, determine diagenetic trajectories. Finally, surface reaction has implications for our ability to constrain fractionation factors in experimental and natural systems. The experimental observations suggest that exchange between tests and solution is nominal over ∼100 days. Experiments aimed at deducing fractionation factors rely on the equilibration of bulk solid and fluid, since these are the readily analyzed reservoirs. We quantify the fraction of carbonate (>5%) that must react so that surface reaction does not impact the interpretation of Ca isotopic fractionation factors, and discuss the implications for more “fluid-dominated” elements such as Mg and O.

Features of the dimerization equilibrium in square-well fluids

We have analyzed chemical equilibria in dimerizing fluids where the pair interactions between monomers and dimers are described by square-well potentials of varying depths and widths. The association is limited by the dimerization stage, in which the dimer is a sphere circumscribed around overlapping monomers. The distances between their centers correspond to the bond lengths. The dissociation energy is considered as a parameter of the theory. Within the statistical-thermodynamic model of the chemical reaction in fluid phase inevitable volume changes in associative equilibria were also taken into account by means of a consistent equation of state (EoS). We show that the attractive part of the intermolecular interaction can manifest itself in deviations of the chemical equilibrium from ideality alternative with temperature. The influence of the attraction and repulsion between monomers and dimers on the position of associative equilibrium is different at high and low temperatures. The stronger the attraction between monomers and (or) the weaker the attraction between associates, the more the equilibrium shifts towards dissociation (especially at moderate temperatures). The changes in density were analyzed as a function of the variation of the square-well depth and width in the associated mixture as well. The increase in the packing fraction is most pronounced with an increase in the width, describing the attraction between the dimers, particularly in the case of small bond lengths. With this, the square-well attraction, in particular between the dimers, contributes to an additional ordering of the fluid.

Коэффициенты распределения РЗЭ+Y между минералами и охлаждающимся богатым сульфатной серой флюидом (термодинамическое моделирование)

Актуальность работы обусловлена тем, что изучение коэффициентов распределения РЗЭ+Y между минералами-концентраторами этих элементов и между минералами и сульфатными флюидами в различных щелочных и слабокислых системах позволяет получить недостающие параметры, необходимые для моделирования процессов кристаллизации и рудогенеза в пределах карбонатитовых рудно-магматических систем. Для определения механизмов концентрирования рудных компонентов важнейшим является выявление главных и второстепенных минералов-концентраторов редких элементов. Цель работы: оценить коэффициенты распределения лантаноидов +Y между РЗЭ-содержащими минералами и между этими минералами и равновесными с ними гидротермальными флюидами в слабокислых и слабощелочных условиях при температуре 500-100 °С и давлении 2000-125 бар. Методы: термодинамическое моделирование взаимодействия монацита и кальцита с гидротермальными флюидами с применением программного комплекса HCh (разработчик Ю.В. Шваров). Для определения состояния равновесия в алгоритме программы использован метод минимизации свободной энергии Гиббса системы (программа GIBBS) в комплексе с базой термодинамических данных UNITHERM. Результаты. Показано, что коэффициенты распределения РЗЭ+Y между минералами большей частью не зависят от кислотно-щелочной обстановки минералообразования. Кислотность-щелочность флюидов заметно сказывается только на распределении РЗЭ между флюоритом и фторапатитом. Основное влияние на фракционирование РЗЭ оказывает температура и сопряженные с нею параметры. Только для пары монацит/РЗЭ-флюорит понижение температуры способствует росту величин коэффициентов распределения, т. е. вхождению РЗЭ в монацит. В парах монацит/РЗЭ-фторапатит, ксенотим/РЗЭ-фторапатит и в кислых условиях в паре РЗЭ-флюорит/РЗЭ-фторапатит понижение температуры сопровождается уменьшением величин коэффициентов распределения и способствует некоторому обогащению фторапатита редкими землями. Kd минерал/флюид для монацита, ксенотима и РЗЭ-флюорита выше единицы и это означает, что при охлаждении равновесного флюида РЗЭ+Y преимущественно концентрируются в этих минералах.

The Discussion About Rational Pressure Limit of Four Strip in The North Intermediate Zone of SaBei

Based on material equilibrium and mechanics of fluid through porous media principle, this paper analyzes formation pressure and the degree that all kinds of influencing factors to it by using basic physics knowledge, it also discusses how to establish rational pressure limit, which presents references to harness effect and controls validly to the formation pressure of intermediate zone in Sabei.

Non-Abelian anomalous (super)fluids in thermal equilibrium from differential geometry

We apply differential geometry methods to the computation of the anomaly-induced hydrodynamic equilibrium partition function. Implementing the imaginary-time prescription on the Chern-Simons effective action on a stationary background, we obtain general closed expressions for both the invariant and anomalous part of the partition function. This is applied to the Wess-Zumino-Witten action for Goldstone modes, giving the equilibrium partition function of superfluids. In all cases, we also study the anomaly-induced gauge currents and energy-momentum tensor, providing explicit expressions for them.

Quantifying structural dynamic heterogeneity in a dense two-dimensional equilibrium liquid.

We investigate local structural fluctuations in a model equilibrium fluid with the aim of better understanding the structural basis of locally heterogeneous dynamics identified in recent simulations and experimental studies of glass-forming liquids and other strongly interacting particle systems, such as lipid membranes, dusty plasmas, interfacial dynamics of crystals, the internal dynamics of proteins, etc. In particular, we utilize molecular dynamics simulation methods to study a single component Lennard-Jones condensed material at constant temperature in two dimensions over a range of densities covering both liquid and crystalline phase regimes. We identify three distinct structural classes of particles by examining the immediate neighborhood of individual particles relying on a solid-angle based tessellation technique. The area distribution of the neighborhoods reveals cages having hexagonal, pentagonal, and square symmetries. Pentagonal cells appear to be the predominant motif in the liquid phase, while the solid phase is dominated by hexagonal cells, as in the case of a perfect crystal. An examination of the spatial organization of particles belonging to each structural class further indicates that finite-size clusters of the hexagonal and pentagonal particle populations arise within both liquids and solids, and the size of these clusters grows in a complementary way as a function of density. Both particle populations form percolation clusters in the liquid-crystal coexistence regime. Interestingly, the populations of particles with different local structures, defined by the arrangement of neighboring particles, are found to maintain different diffusivities, as computed from the velocity autocorrelation function for each type of particle for all densities studied. Our analysis provides a new conceptual framework for understanding the structural origin of dynamical heterogeneity in soft materials.

The Breakdown of the Fluid Approximation for Electrons in a Plasma Wake

AbstractA comparative study using a fluid‐based analytic solution, hybrid particle‐ion fluid‐electron particle‐in‐cell (PIC), and fully kinetic PIC is carried out to examine a collisionless, mesothermal plasma flow over a large, unbiased plate. We find that the plasma wake may be characterized into two regions based on the electron characteristics: a fluid electron expansion region and a kinetic electron expansion region. In the fluid electron expansion region, the electrons may be considered to be an equilibrium fluid and all the three approaches lead to a similar result. In the kinetic electron expansion region, the local electron velocity distributions are strongly non‐Maxwellian and the commonly used fluid approximation for electrons breaks down. The results also show that the error of the hybrid PIC simulation strongly correlates with a nonequilibrium parameter based on the weighted deviation of the electron velocity distribution from the equilibrium.

Experimental Study of the SiO2–H2O–KF–KCl–NaF System at 700–800°C and 1–2 kbar Based on Synthetic Fluid Inclusions in Quartz

The phase state of the fluid in the H2O–KF ± KCl ± NaF system is studied in the presence of quartz for an experimental assay of the mutual influence of various salts of the fluid-forming mixture on heterogeneous fluid equilibria. The fluid inclusions were synthesized in quartz by the fracture healing method from solutions with KF + KCl and KF + NaF mixtures at 1 or 2 kbar and 700, 750, or 800°C. The results of the fluid inclusion study indicate a heterogeneous state of the fluid and variation in the fluid composition during experiments as a result of its interaction with quartz. The increase in temperature and pressure, as well as variation in the proportions of the salt contents in the fluid-forming mixture, changed the course of chemical reactions. After all the experiments, a glassy phase was observed in some types of inclusions. It is known that aqueous KF or KCl solutions, the solubility of which increases during heating, are characterized by phase equilibria of systems of the first type (Valyashko, 1990), when liquid and vapor are equilibrated for a heterogeneous state of the fluid. In this case, some inclusions should homogenize to vapor. However, no similar inclusions were observed in contrast to denser fluid phases (liquids), which are typical of the upper heterogeneous area of systems of the second (P–Q) type. Some inclusions host solid phases, the solubility of which decreases as the temperature increases. The results of experiments in the presence of KF + NaF solutions showed that the amount of inclusions of heterogeneous entrapment increases at higher temperatures simultaneously with a decrease in the H2O content of the glassy phase.

Evidence of polygenetic carbon trapping in the Oman Ophiolite: Petro-structural, geochemical, and carbon and oxygen isotope study of the Wadi Dima harzburgite-hosted carbonates (Wadi Tayin massif, Sultanate of Oman)

The Wadi Dima area (Oman Ophiolite) exposes partially altered to highly serpentinized harzburgites that are cross-cut by intense (>20 Vol%) carbonate veining. We identified a sequence of 3 types of carbonate veins with compositions ranging from calcite to dolomite (Mg/Ca = 0-0.85). Type 1 carbonates occur as a fine diffuse vein network, locally replacing olivine cores, penetrative into the serpentinized harzburgites. They have depleted trace elements abundances (e.g., Yb < 0.2 × C1-chondrite) relative to other Wadi Dima carbonates, exhibit negative Ce and positive Y, U anomalies and a broad range in δ13CV-PDB (-5 to -15‰) and δ18OSMOW (18 to 31‰). These compositions are consistent with precipitation after seawater-derived fluids and/or fluids in equilibrium with mantle rocks and serpentines during cooling of oceanic lithosphere (110 to 15°C). Type 2 carbonates are localized in veins, which acted as main flow paths for fluids interacting with peridotites in the exhumed Oman mantle lithosphere (50°C-10°C). The orientation of these veins is controlled by the crystallographic anisotropy of Oman mantle peridotites. Type 2 carbonates record two stages. The first involved the formation of large calcite crystals of composition similar to Type 1 carbonates (trace element depleted; δ13CV-PDB B = -4 to -9‰ and δ18OSMOW = 26 to 30‰), which during the second stage were recrystallized to form dolomite and calcite microcrystals (trace element enriched; δ13CV-PDB = -7 to -13‰ and δ18OSMOW = 29 to 32‰), after fluids sampling different sources including contributions of sediment-derived components. They were most likely formed at shallow depths and record the transition from oceanic to continental settings during late Cretaceous ophiolite obduction. Type 3 veins reactivate Type 2 veins. They comprise dominantly calcite and dolomite microcrystals (Light REE enriched patterns) with isotopic compositions (δ13CV-PDB B ~ -7 to -8‰; δ18OSMOW~ 28 to 32‰) consistent with precipitation at low temperatures (T°<30°C) from surface/meteoric fluids. Type 3 veining is probably triggered by ophiolite uplift during the Oligocene to early Miocene. Our study presents new insights into the role of the initial mantle anisotropy in the orientation of the vein network and of principal flow paths during serpentinization and carbonatization of mantle peridotites. It also highlights the highly variable carbon isotope composition of carbonates and suggest different origins for these heterogeneities: the carbon isotope composition of the early Type 1 carbonates dispersed in the poorly connected peridotites is locally modified by serpentinization reactions whilst the carbon isotope compositions of Type 2 and 3 carbonates record mixing of fluids from different sources in high flow veins.

Silicate solution, cation properties, and mass transfer by aqueous fluid in the Earth\u2019s interior

Aqueous fluids in the Earth’s interior are multicomponent systems with silicate solubility and solution mechanisms strongly dependent on other dissolved components. Here, solution mechanisms that describe the interaction between dissolved silicate and other solutes were determined experimentally to 825 °C and above 1 GPa with in situ vibrational spectroscopy of aqueous fluid while these were at high temperature and pressure. The silicate content in Na-bearing, silicate-saturated aqueous fluid exceeds that in pure SiO2 at high temperature and pressure. Silicate species were of Q0 (isolated SiO4 tetrahedra) and Q1 (dimers, Si2O7) type. The temperature dependence of its equilibrium constant, K = XQ1/(XQo)2, yields enthalpies of 22 ± 12 and 51 ± 17 kJ/mol for the SiO2–H2O and Na-bearing fluids. In contrast, in Ca-bearing fluids, the solubility is more than an order of magnitude lower, and only Q0 species are present. The present data together with other published experimental information lead to the conclusion that the silicate solubility in aqueous fluids in equilibrium with mafic rocks such as amphibolite and peridotite is an order of magnitude lower than the solubility in fluids in equilibrium with felsic rocks such as andesite and rhyolite compositions (felsic gneiss) under similar temperature and pressure conditions. The silicate speciation also is more polymerized in the felsic systems. This difference is also why second critical end-points in the Earth are at lower temperature and pressure in felsic compared with mafic systems. Alkali-rich fluids formed by dehydration of felsic rocks also show enhanced high field strength element (HFSE) solubility because alkalis in such solution form oxy complexes with the HFSE cations. Fluids formed by dehydration of felsic rocks in the Earth’s interior are, therefore, more efficient transport agents of silicate materials than fluids formed by dehydration of mafic and ultramafic rocks, whether for major, minor, or trace elements.

Composition of Hydrocarbons in Synthetic Diamonds Grown in a Fe—Ni—C System (according to Gas Chromatography—Mass Spectrometry Data)

The first data of chromatography—mass spectrometry analysis of volatiles from crystals of synthetic diamonds grown in a Fe—Ni—C system at 1350–1400°С and 5.5–6.0 GPa are presented. The composition of the fluid in equilibrium with the metal-carbon melt is determined, and a comparative estimation for the compounds of different hydrocarbons and their derivatives is made. It is shown that a significant role in these processes is played by high-molecular-weight hydrocarbons; and the total share of hydrocarbons and their derivatives in the fluid compounds can exceed 86%.

Chemical and isotopic signatures of hot springs from east-central Sonora State, Mexico: a new prospection survey of promissory low-to-medium temperature geothermal systems

A promissory low-to-medium temperature geothermal system located in Sonora (Mexico) has been studied. In the present work, a detailed geochemical survey was carried out to understand the hydrogeochemical signatures of hot spring waters. A field work campaign was conducted for collecting water samples from twelve hot springs placed in four major zones (NW, NE, C, and S). The collected samples were analysed by chemical and isotopic methods for determining their chemical (major and trace elements) and isotopic (18O/16O and D/H) compositions. Using geochemometric analyses of the fluid composition and fractionation, depletion and enrichment processes exhibited by major and trace elements were analysed.&#x0D; Hydrogeochemical classification was used to indicate the presence of sodium-sulphate (Na-SO4) waters in the North (NW and NE) and South hydrothermal zones; whereas calcium-magnesium-bicarbonate (Ca-Mg-HCO3) waters were identified for the Central zone. Some hot spring waters located in the NE zone were also typified as sodium-bicarbonate (Na-HCO3). In relation to the isotopic signatures of 18O/16O and D/H, four water samples from NE and C zones lie near to the global meteoric water line; whereas the remaining eight samples showed a shift for both oxygen and deuterium isotopes. A mixing line with a small shift of δ18O was identified and used as a proxy to discriminate waters with different isotopic signatures.&#x0D; After applying a geochemometric outliers detection/rejection and an iterative ANOVA statistical test, the mean temperature inferred from the most reliable solute geothermometers was 149±40 °C, which suggests to be considered as the minimum value of the reservoir temperature. As most of the hot spring waters fall outside of the full equilibrium curve, the original reservoir conditions were corrected by using a mixing conductive model, which predicted a deep equilibrium temperature of 210±11 °C. As this temperature is considerably higher than the mean temperature inferred from the geothermometers, it was suggested as an optimistic maximum reservoir temperature of the Sonora geothermal system.&#x0D; Using 150 °C and 200 °C as rounded-off reservoir temperatures (or min-max estimates), geochemical equilibria modelling based on fluid-mineral stability diagrams was carried out. An equilibrium process among local hydrothermal waters and albite-potassium feldespar and muscovite-prehnite-laumontite mineral assemblages was found. These minerals were proposed as representative mineral assemblages of low-grade metamorphism, which seems to indicate that the geothermal fluid equilibria were probably reached within the intermediate to acidic volcanic rocks from the Tarahumara Formation.

Structural crossover in a model fluid exhibiting two length scales: Repercussions for quasicrystal formation.

We investigate the liquid state structure of the two-dimensional model introduced by Barkan etal. [Phys. Rev. Lett. 113, 098304 (2014)10.1103/PhysRevLett.113.098304], which exhibits quasicrystalline and other unusual solid phases, focusing on the radial distribution function g(r) and its asymptotic decay r→∞. For this particular model system, we find that as the density is increased there is a structural crossover from damped oscillatory asymptotic decay with one wavelength to damped oscillatory asymptotic decay with another distinct wavelength. The ratio of these wavelengths is ≈1.932. Following the locus in the phase diagram of this structural crossover leads directly to the region where quasicrystals are found. We argue that identifying and following such a crossover line in the phase diagram towards higher densities where the solid phase(s) occur is a good strategy for finding quasicrystals in a wide variety of systems. We also show how the pole analysis of the asymptotic decay of equilibrium fluid correlations is intimately connected with the nonequilibrium growth or decay of small-amplitude density fluctuations in a bulk fluid.

Iron isotope fractionation during magmatic-hydrothermal evolution: A case study from the Duolong porphyry Cu-Au deposit, Tibet

Ore-forming fluids ultimately precipitate Fe-bearing sulfides and oxides in hydrothermal ore deposits and the Fe isotopic composition of these minerals can trace magmatic-hydrothermal evolution. Here, we report on the Fe isotopic compositions of a suite of hydrothermal minerals (magnetite, pyrite, and chalcopyrite) and granodiorite porphyry from the giant Duolong porphyry Cu-Au deposit (Bolong and Duobuza section), central Tibet. Most magnetite grains with potassic alteration show only minor δ57Fe variation (0.38 ± 0.07‰ to 0.52 ± 0.04‰ in Bolong and 0.68 ± 0.02‰ to 0.77 ± 0.08‰ in Duobuza), consistent with the equilibrium fluid δ57Fe (∼−0.3‰ and ∼−0.1‰, respectively) at ∼550–480 °C. The equilibrium fluids have lighter Fe isotope signatures than the Duolong granodiorite porphyry (δ57Fe = 0.03 ± 0.06‰ to 0.07 ± 0.02‰), corroborating the hypothesis that exsolved fluids should have a lighter Fe isotopic composition relative to parental magmas. Chalcopyrite from the mineralized Bolong and Duobuza porphyries have relatively consistent δ57Fe values of −0.60 ± 0.07‰ to −0.42 ± 0.07‰ and −0.40 ± 0.08‰ to −0.30 ± 0.05‰, respectively, with equilibrium fluids at ∼450–350 °C having lighter δ57Fe values of ∼−0.7‰ and ∼−0.6‰. The trend of decreasing δ57Fe values in evolved fluids likely reflects Rayleigh fractionation of magnetite enriched in heavy Fe isotopes. This supposition is supported by the lighter δ57Fe value (0.25 ± 0.07‰) recorded in magnetite that equilibrated with a lighter δ57Fe fluid (∼−0.5‰) at ∼470 °C. Compared to chalcopyrite, pyrite from the Bolong and Duobuza sections have heavier δ57Fe values of 0.35 ± 0.06‰ to 0.71 ± 0.06‰ and 0.53 ± 0.06‰ to 0.71 ± 0.07‰, respectively. The pyrite values correlate variably with the Fe isotopic composition of ore-forming fluids (δ57Fe = −0.6‰ to −0.7‰), likely due to variations in the degree of Fe isotope exchange between pyrite and fluid. Moreover, combined with previously published Fe isotopic compositions of hydrothermal minerals from oxidized and reduced ore deposits, the results show that chalcopyrite in oxidized hydrothermal deposits always has a lighter Fe isotopic composition than chalcopyrite from reduced hydrothermal deposits. This is likely controlled by melt composition and precipitation of magnetite/pyrrhotite-bearing mineral assemblages. Therefore, the Fe isotopic composition of chalcopyrite could be a useful diagnostic tool for distinguishing oxidized from reduced fluids in hydrothermal systems.

The partitioning of chalcophile elements between sediment melts and fluids at 3 GPa, 950–1050 °C with implications for slab fluids in subduction zones

There is growing evidence for the importance of slab sediment components in transferring trace element signatures to the arc mantle. The chalcophile elements are of particular interest due to their differing compatibility in sulfide and sulfate phases, the stability of which are dependent on subducted sediment redox. Many studies have shown that chalcophile elements are compatible in saline fluids at shallow levels of arcs (<10 km depth) but there is comparatively limited work on chalcophile element fluid partitioning at deeper conditions relevant to subduction. We performed experiments at 3 GPa and 950–1050 °C on fluid-saturated pelite melt compositions doped with S, V, Sc, Ce, Mo, As, Sb and Pb at reduced and oxidized conditions where pyrrhotite (Po) and anhydrite (Anh) are stable, respectively. We determined the trace element composition of quenched melts in our fluid-saturated experiments by LA-ICP-MS and derive the coexisting fluid composition by mass balance. The concentration of lithophile elements V and Sc in melts and fluids are unaffected by redox, however Ce concentration is higher in melts and lower in fluids when Po rather than Anh is stable. Of the chalcophile elements, S is in higher concentration in the melts and fluids when Anh is stable compared to Po. Molybdenum, As, Sb and Pb, are enriched in melt and depleted in fluid in the presence of Anh. The partition coefficients determined for these elements are the first reported at 3 GPa in reduced fO2 conditions where Po is present (at 1000 °C, Dfluid/melt Ce = 4 ± 0.3, Dfluid/melt Mo = 319 ± 43, Dfluid/melt As = 669 ± 134, Dfluid/melt Sb = 1437 ± 208, Dfluid/melt Pb = 73 ± 4; all errors are 1σ) and in oxidized conditions where Anh is present (at 1000 °C, Dfluid/melt Ce = 150 ± 48, Dfluid/melt Mo = 3.7 ± 1.9, Dfluid/melt As = 2.5 ± 1.7, Dfluid/melt Sb = 12 ± 5.1, Dfluid/melt Pb = 3.8 ± 1.8). The contrasting behavior of Mo and Ce in fluids versus melts is consistent with the notion that elevated Mo in lavas from the Lesser Antilles arc is associated with reduced fluids extracting Mo from subducted black shales. The Mo/Ce ratio is a promising tool in other arcs to infer the role that fluid may or may not play for chalcophile enrichment in the sub-arc mantle. Unlike melts, fluids in equilibrium with reduced, Po-bearing sediments can endow the arc mantle in chalcophile elements without concomitant oxidation.

Towards a More Earth‐Like Circulation in Idealized Models

AbstractIdealized models are useful for the investigation of dynamical phenomena in which physical processes play a secondary role. Typically, such models employ highly idealized topography and zonally symmetric equilibrium temperatures as forcings. However, these simplifications are somewhat unrealistic and make these models unfit for investigations in which similarity with the real atmosphere is crucial. In this study, we present a new idealized model of the stratosphere‐troposphere system which has a more Earth‐like circulation than previous models. We accomplish this by introducing into the dry dynamical core of the Geophysical Fluid Dynamics Laboratory realistic topography and equilibrium temperatures with zonal asymmetries. We then explore the model's sensitivity to the prescribed strength of the surface momentum drag. We find improvements in the model's circulation when validating against reanalysis. Most notably, the strength and structure of the winds, the spectrum of planetary waves, and the frequency of stratospheric sudden warming events are more realistic than in traditional idealized models. In the extratropics, the diagnosed diabatic forcing of the model also compares favorably against the observations. We further find that variations in the surface momentum damping exert an important control on the model's circulation, including the frequency of stratospheric sudden warming events. We believe that the new model reduces the gap between traditional idealized models and full models and that it is useful for the investigation of phenomena in which greater similarity with the real system is needed. The code for the new model and its equilibrium temperature data set is published on GitHub.

Stable isotope and fluid inclusion study of sediment-hosted stratiform copper deposits from the Neuquén Basin, Argentina

The Los Chihuidos and El Porvenir deposits of the Neuquen Basin are examples of sediment-hosted stratiform Cu deposits generated by interaction of hydrocarbons and formation water with host red beds and metal-charged basinal brines. During early diagenesis of red beds precipitated hematite, kaolinite at 60 °C from meteoric water followed by calcite 1 (δ13C − 8 to − 3.3‰) and barite (δ34S + 4.1‰) with increasing temperature (75–85 °C) from an evolved surface fluid (δ18Ofluids + 0.9 to + 2.7‰). During the Tertiary Andean orogeny, hydrocarbons and formation water migrated and reacted with the red beds resulting in bleaching of the sandstone. Smectite (fluid δ18O − 2.2‰ and δD − 73.7‰), chlorite-smectite mixed-layer minerals (fluid δ18O − 6.9‰ and δD − 84‰), pyrite (δ34S + 10.2‰), and calcite 2 (δ13C − 12.9 to − 6.8‰) formed as by-product of the redox reactions. Calcite 2 formed from low-salinity fluids (0.4 to 5.9 wt% NaCl equiv.) at slightly higher temperatures (125–145 °C) at El Porvenir and at Los Chihuidos deposit (80–105 °C). During subsequent uplift, metal-charged basinal brines flowed into the bleached sandstone and precipitated chalcopyrite-bornite (δ34S + 12.3‰) followed by chalcocite-spionkopite (δ34S − 64 to + 4.1‰). Calcites 3a (δ13C − 19 to − 10.1‰) and 3b (δ13C − 31.4 to − 9.5‰) that accompanied Fe-Cu and Cu sulfides, respectively, formed from saline fluids (up to 21.3 wt% NaCl equiv.) at temperatures of 159–70 °C. The δ18O values (+ 5.6 to + 11.4‰) of fluids in equilibrium with calcite 3a are similar to oilfield and basinal brines. Fluids in equilibrium with calcite 3 in Los Chihuidos and calcite 3b in El Porvenir show much lighter δ18O values (− 7.3 to − 4.6‰ and − 0.6 to + 2.3‰, respectively), which suggests the involvement of methane as the main reductant and possibly meteoric water interaction.