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The redox state of the convective asthenospheric mantle governs the speciation of volatile elements such as carbon and, therefore, influences the depth at which (redox) melting can occur, with implications for seismic signals. Geophysical observations suggest the potential presence of carbonatite melts at a depth of 200–250 km. However, thermodynamic models indicate that the onset of (redox) melting would occur at 100–150 km for a mantle with 3%–4% of Fe3+/∑Fe. Here, we present a new oxybarometer that is based on the V/Sc exchange coefficient between olivine and the melt, which is insensitive to surficial alteration, volatile degassing, electron exchange reactions and fractional crystallization. By applying this method to primary mid‐ocean ridge basalts (MORBs) from Southwest Indian Ridge and East Pacific Rise, we demonstrate that the average oxygen fugacity (fo2) of MORBs corrected for the depth of formation is 0.78 ± 0.26 (1σ) log units above the fayalite‐magnetite‐quartz (FMQ) buffer, which is slightly more oxidized than previously estimated (near FMQ buffer). Our findings indicate that the convective asthenospheric mantle exhibits higher oxygen fugacity than the continental lithospheric mantle. Along an adiabat, carbonatitic melts can form from a CO2‐bearing source at a depth of 200–250 km, explaining the asthenospheric mantle's electrical conductivity and seismic velocity anomaly. Plain Language Summary: The oxidized form of carbon, carbonate, plays a pivotal role in the melting of the deep mantle by substantially lowering the mantle solidus and instigating the formation of carbonatite melt. The presence of a high‐conductivity and seismic low‐velocity layer at depths of 220–300 km in the asthenospheric mantle suggests the presence of carbonatite melts. Nevertheless, the traditional view posits that the asthenospheric mantle at these depths is reduced, with carbon primarily in the form of diamonds, making it unlikely to induce mantle melting and carbonatite melt formation. In this study, we present a novel oxybarometer based on the V/Sc exchange coefficient between olivine and melt and calculate the oxygen fugacity of the Southwest Indian Ridge and East Pacific Rise MORBs. Our findings reveal that global MORBs and their mantle sources are more oxidized than previously thought. In such an oxidized environment, the conversion of diamond to carbonate and the formation of carbonatite melts occur at depths of 220–250 km, providing a reasonable explanation for the high conductivity and low‐velocity layer in the deep asthenosphere. Key Points: The exchange of V/Sc between the olivine and melts can serve as a robust oxybarometerMid‐ocean ridge basalts are oxidized with oxygen fugacity of FMQ + 0.46 ± 0.26Carbonatitic melts can form at a depth of 200–250 km beneath mid‐ocean ridges [ABSTRACT FROM AUTHOR]

The Surface Ocean CO2 Atlas (SOCAT) of CO2 fugacity (fCO2) observations is a key resource supporting annual assessments of CO2 uptake by the ocean and its side effects on the marine ecosystem. SOCAT data are usually released with a lag of up to 1.5 years which hampers timely quantification of recent variations of carbon fluxes between the Earth System components, not only with the ocean. This study uses a statistical ensemble approach to analyze fCO2 with a latency of one month only based on the previous SOCAT release and a series of predictors. Results indicate a modest degradation in a retrospective prediction test for 2021–2022. The generated fCO2 and fluxes for January–August 2023 show a progressive reduction in the Equatorial Pacific source following the La Niña retreat. A breaking‐record decrease in the northeastern Atlantic CO2 sink has been diagnosed on account of the marine heatwave event in June 2023. Plain Language Summary: There is a growing need to monitor carbon emissions and removals over the globe in near real time in order to correctly interpret changes in CO2 concentrations as they unfold. For the oceans, the best information comes from measurements of the surface ocean CO2 fugacity (fCO2) by the international marine carbon research community. So far, this data is mostly available 6 to 18 months behind real time after collection, qualification, harmonization, and processing. Here, we show that a set of biological, chemical, and physical predictors available in near real time, allows the information contained in the "old" fCO2 measurements to be transferred over time. Based on a statistical technique, we combine all these data sources to estimate global monthly maps of fCO2 and of CO2 fluxes at the air‐sea interface within one month behind real time and with good accuracy. Key Points: We demonstrate the capacity of statistical models to generate global maps of fCO2 and air‐sea flux with a latency reduced to one monthA decrease in the CO2 source for January to August 2023 diagnosed in the tropical Pacific coheres with the retreat of the La Niña eventAn unusual northeastern Atlantic sink reduction diagnosed for June 2023 is linked to record heat and exceptionally low winds [ABSTRACT FROM AUTHOR]

In this study, we systematically investigate electrochemical hydrogen charging conditions equivalent to hydrogen gas pressures relevant for hydrogen transportation in X65 pipeline steel. By performing hydrogen gas permeation, a relationship for Sieverts' law was established, which was used in combination with electrochemical hydrogen permeation to determine the equivalent hydrogen pressure. The results revealed that cathodic protection simulated condition at –1050 mVAg/AgCl was equivalent to a hydrogen pressure of 12.3 bar. The addition of thiourea, a hydrogen recombination poison, and changing the applied potential in the cathodic direction increased the equivalent hydrogen pressure. In this way, an electrochemical charging condition equivalent to a potential hydrogen gas pressure for hydrogen transportation (200 bar) was determined. [ABSTRACT FROM AUTHOR]

Mass transfer across the crust‐mantle boundary is a fundamental process governing planetary differentiation, the evolution of geochemical reservoirs and ore formation, controlled by physicochemical conditions at the crust‐mantle interface. In situ trace‐element, clinopyroxene 87Sr/86Sr and garnet Fe3+/ΣFe of kimberlite‐borne eclogite xenoliths from the deep (∼50 km) crust‐mantle transition below the ca. 1.2–1.0 Ga Namaqua‐Natal Fold Belt (southwestern Kaapvaal craton margin) were determined to elucidate their origin and evolution, and to constrain the oxygen fugacity of this pivotal but largely inaccessible environment. Based on a garnet source signature (NMORB‐normalized Er/Lu > 1) in pristine "gabbroic" eclogites with pronounced positive Eu, Sr, and Pb anomalies, the suite is interpreted as originating as plagioclase‐rich cumulates in oceanic crust from melts generated beneath mature oceanic lithosphere, subsequently subducted during the Namaqua‐Natal orogeny. Enriched eclogites have higher measured 87Sr/86Sr in clinopyroxene (up to 0.7054) than gabbroic ones (up to 0.7036), and show increasing bulk‐rock Li, Be and Pb abundances with increasing δ18O in clinopyroxene, and muted Eu‐Sr‐Pb anomalies. These systematics suggest interaction with a siliceous fluid sourced from seawater‐altered oceanic sediment in a subduction mélange setting. Garnet Fe3+/ΣFe in deep crustal eclogites is extremely low (0.01–0.04, ±0.01 1σ), as inherited from the plagioclase‐rich cumulate protolith, and owing to preferred partitioning into clinopyroxene at low temperatures (∼815–1000°C). Average maximum oxygen fugacities (∆logƒO2(FMQ) = −3.1 ± 1.0 to −0.5 ± 0.7 relative to the Fayalite‐Magnetite‐Quartz buffer) are higher than in deeper‐seated on‐craton eclogite xenoliths, but mostly below sulfate stability, limiting the role of S6+ species in oxidizing the mantle wedge. Plain Language Summary: Subduction zones represent the main interface between Earth's surface and its deep interior. Metamorphic reactions during subduction cause fluid or melt loss from seawater‐altered oceanic crust and sediment, which enriches the overlying mantle, and possibly oxidizes it. This would explain why the mantle sources of subduction zone magmas appear to be more oxidized than in other tectonic settings. However, the details of the mass transfer in this deep environment are difficult to constrain because it is inaccessible. Using rare deep‐seated magmas (kimberlites) as probes of a ca. 1.2 billion year old southern African subduction zone, we investigated eclogite fragments that originated as subducted oceanic crust and were much later plucked from the wallrocks by the ascending magma. These eclogites show elemental and isotopic signatures of interaction with subducted sediments, pointing to mingling processes similar to those observed in modern subduction zones. We also estimated their oxygen fugacity, a measure of the chemical potential of oxygen. We find that sulfur, which has been implicated in mantle oxidation, would have only been stable in these rocks in its reduced form, making even seawater‐altered eclogites sinks rather than sources of oxygen, with implications for the transfer of sulfur‐loving metals across the mantle‐to‐crust‐boundary. Key Points: Eclogite xenoliths sampling deep crust‐mantle transition below Namaqua‐Natal Fold Belt have plagioclase‐rich oceanic protolithsEnriched xenoliths show signatures of interaction with siliceous, subducted sediment‐derived fluids under shallow fore‐arc conditionsFe3+‐based eclogite oxybarometry with oxygen fugacities below sulfate stability limits the role of S6+ species in mantle wedge oxidation [ABSTRACT FROM AUTHOR]

Oxygen fugacity (fO2) is a key intensity variable during the entire magmatic‐hydrothermal mineralization courses. The redox state and its variations between different stages of the ore‐forming fluids of intermediate sulfidation epithermal deposits are rarely deciphered due to the lack of appropriate approaches to determine fO2 of the fluids. Here, we reported the δ34S of the sulfides from three different stages (stage I, II, III) of Zhengguang, an Early Ordovician Au‐rich intermediate sulfidation (IS) epithermal deposit, to decipher the redox evolution of the ore‐forming fluids. The increasing δ34S values from stage I pyrite (py1, average –2.6‰) through py2 (average –1.9‰) to py3 (average –0.2‰) indicates a decrease of the oxygen fugacity of the ore‐forming fluids. A compilation of δ34S values of sulfides from two subtypes of IS deposits (Au‐rich and Ag‐rich) from NE China shows that the δ34S values of sulfides from Au‐rich IS deposits are systematically lighter than those of Ag‐rich IS Ag‐Pb‐Zn deposit, indicating the ore‐forming fluids of the former are more oxidized than the latter. We highlight that sulfur isotopic composition of hypogene sulfides is an efficacious proxy to fingerprint the oxygen fugacity fluctuations of epithermal deposits and could potentially be used to distinguish the subtypes of IS deposits. [ABSTRACT FROM AUTHOR]

Volatile element abundance is a crucial factor triggering mineralization and controlling the enrichment of molybdenum in porphyry deposits. The Chalukou deposit is the largest porphyry Mo deposit in NE China, with an average grade of 0.087% Mo. In this contribution, we present petrology, bulk geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes, and apatite geochemistry for the Chalukou deposit. The intrusive rocks include pre‐mineralization monzogranite, syn‐mineralization quartz porphyry, fine‐grained porphyry and granite porphyry, and post‐mineralization monzogranite and feldspar porphyry. These granitoids are metaluminous to peraluminous, and belong to alkali‐calcic to calc‐alkalic series. Zircon εHf(t) values of granitoids range from +0.2 to +5.7 with corresponding Hf crustal model ages of 805–1170 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle‐derived magma. They are characterized by logf(O2) of −16.1 to −9.4, with an average of −12.5, ΔFMQ of +0.8 to +7.9, with an average of +4.5, showing a relatively high oxidation state for the syn‐mineralization magma. The apatites in quartz porphyry have the highest F contents, ranging from 3.61 to 4.62 wt%. At Chalukou, F‐rich magma is conducive to the convection of magma and promotes the efficient separation of differentiation magma, making the magmatic‐hydrothermal fluid circulate many times, eventually resulting in the accumulation of ore‐forming materials on the top of the magma chamber and gradually aggravating mineral enrichment processes. [ABSTRACT FROM AUTHOR]

This study presents the first reconstruction of the smelting conditions in 16th‐ to 18th‐century smelters from Miedziana Góra (Holy Cross Mountains, Poland). Based on geochemical (inductively coupled plasma mass spectrometry/emission spectrometry, X‐ray fluorescence) and mineralogical analysis (X‐ray diffractometry, scanning electron microscopy, electron probe micro‐analysis) of historical slags, their chemical/phase composition and the basic smelting parameters (temperature, melt viscosity, and oxygen fugacity) were determined. Due to the differences in chemical and phase composition, slags from different smelting stages have been distinguished: hypocrystalline slags (MG6) from speiss/matte production and glassy (MG1–MG5) from matte conversion. In glassy slags, pyroxenes, quartz/cristobalite grains, and aggregates composed of metallic Cu and PbO are dispersed in the glass. Hypocrystalline slags are composed of wollastonites, anorthites, and metallic Cu. The temperature range at which the slags were formed was from ~1100°C (solidus temperature) to 1150–1200°C (liquidus temperature). The silicate melt's viscosity was from log η = 1.19 to 4.42 Pa s (at 1100–1200°C). The higher viscosity of MG1–MG5 slags indicates that, unlike MG6 slags, they were not formed during gravity separation. Information about the phase composition made it possible to determine the oxygen fugacity in the range of log fO2 = −4 to −12 atm. High oxygen fugacity indicates the oxidizing nature of the smelting process. [ABSTRACT FROM AUTHOR]

The Hongshishan chromitite deposits are situated to the north of the Beishan orogenic collage, in the southern part of the Central Asian Orogenic Belt. This study describes the mineral chemistry, Re‐Os isotopes and platinum‐group elements geochemistry of the Hongshishan chromitites for the purpose of constraining the origin, evolution and composition of their parental melts. The restricted ranges of Al2O3, Cr2O3 and Cr#‐Mg# variation of chromite‐cores and chromites fall within the field of the mid‐ocean ridge and ophiolitic podiform chromite settings. The (187Os/188Os)i ratios of the chromitites are in the range of 0.12449–0.12745 (average 0.12637) and the γOs are from –1.92 to –0.06 (average –0.83). In the Re‐Os isotope diagrams, all the samples fall in the field of chromitites and show a residual peridotitic trend. The range of Os isotopic compositions and γOs values indicate that they overlap the depleted MORB mantle (DMM) as well as being close to global Os isotopic data and γOs of ophiolite chromitites. The characteristics of the PGE contents can be roughly subdivided into two groups: podiform chromitites and Ural‐Alaskan type complexes. For the ferritchromite cores, the calculated Al2O3 concentrations of the parental melt are higher (average 16.65 wt%) in high‐Cr than high‐Al chromitite (average 16.17 wt%) and for the chromite, the calculated Al2O3 concentrations are even higher (average 16.48 wt%) in the high‐Cr than the high‐Al examples (average 15.38 wt%). In the (TiO2)melt vs. TiO2 diagrams, most high‐Al melts fall in the MORB, while the high‐Cr melts fall in the ARC field. The calculated FeO/MgO ratios for the parental melt show the closest resemblance to a MORB magma composition. The inferred parental melt composition for studied chromitites falls in the field of mid‐ocean ridge basalt (MORB) magmas and far away from boninite. The calculated degrees of partial melting producing the chromitites are 16%–22% (average 19%), which is around the range of those of the MORB magmas. The chromitites are suggested to have been formed in a MORB setting. The chromites and ferritchromite cores are mostly scattered along the MORB and SSZ harzburgite–dunite fields. Ferritchromite rims and ferritchromites with high YFes formed as a result of alteration during serpentinization.. [ABSTRACT FROM AUTHOR]

PEBAX 2533 membrane is used to investigate plasticization by carbon dioxide (CO2) at low pressure. To reduce complex interaction caused by hydrostatic pressure and competitive sorption, a new experimental technique named the "Rest test" is presented. In the Rest test, the membrane is exposed to permeation of CO2 at 4 bar for 30 min and then put to rest for up to 12 h with residual CO2 after ventilation. When the membrane rests more than 9 h with residual CO2 after the permeation, the permeability increases by, at least, 50%. Permeation of CO2 is the prerequisite condition of permeability increase during the rest. Permeability increase in the Rest test is improved by permeate side purge and prolonged rest period. Fugacity and sorption of leftover CO2 during the rest are the main factors inducing the permeability increase, whereas the permeability increase is suppressed by higher feed pressure and longer CO2 permeation time, indicating the influence of hydrostatic pressure. The Rest test cannot increase the permeability of glassier PEBAX 1657. The findings and relevant factors suggest that low‐pressure plasticization during the rest is a potential source of the permeability increase. [ABSTRACT FROM AUTHOR]

To understand the oxygen fugacity (fO2) during subduction initiation, we examined proto‐arc boninites and associated mantle peridotites from the Troodos ophiolite, Cyprus. The Troodos ophiolite represents an exhumed piece of oceanic lithosphere that formed during subduction initiation in Neo‐Tethys in Late Cretaceous. Dunites and surrounding harzburgites in the Kokkinorotsos podiform chromite deposit of the ophiolite were formed by reactions between peridotites and ascending boninitic magmas. The olivine‐chromite oxybarometers show that the fO2 values (∆QFM −0.41 ± 0.37) of the dunites are slightly higher than those (∆QFM −0.85 ± 0.52) of the harzburgites under mantle conditions, indicating that the mantle fO2 was raised limitedly by percolation of the boninitic magmas. Meanwhile, the boninitic upper pillow lavas in the Margi area also recorded relatively reduced fO2 values (∆QFM −0.52 ± 0.20) during olivine‐chromite crystallization, comparable to the fO2 of mid‐ocean ridge basalts. Shallow‐level processes (i.e., magma ascent, crystallization, crustal assimilation, and degassing) appear to have limited influence on the estimated fO2 values in Troodos. The similarly low fO2 values of the mantle peridotites and boninitic magmas suggest that the Troodos primary boninitic magmas were perhaps not as oxidized as the Izu‐Bonin‐Mariana (IBM) proto‐arc boninitic magmas, though both mantle sources have captured the slab fluids released during subduction inception. This difference might be attributed to the different nature of the slab components (i.e., a more reduced subduction input for Troodos). Our study thus suggests that subducted slabs might not always release oxidized fluids, and the oxidation processes might be different for each nascent subduction zones. Plain Language Summary: Subduction zones have played a key role in mass exchange between the Earth's surface and its interior, and are one of the main factories for the generation of Earth's magmas. The redox state of arc lavas produced at subduction zones controls the formation of important mineral deposits. In fact, subduction zone lavas are believed to be generally more oxidized than mid‐ocean ridge lavas, but the origin of their oxidized nature and how their redox state change during the birth of a subduction zone remains poorly understood. Boninites are special Mg‐ and Si‐rich but Ti‐poor lavas (SiO2 > 52 wt.%, MgO > 8 wt.%, and TiO2 < 0.5 wt.%), and are typical products of magmatism that formed during subduction initiation. Here, we show that the primary boninitic magmas of the Troodos ophiolite of Cyprus are in fact no more oxidized than mid‐ocean ridge basalts, even though their mantle source interacted with the slab fluids released from the incipient subducted plate. Therefore, we propose that proto‐arc magmas, that formed as the down‐going slab began foundering, might not always be oxidized during the inception of a subduction zone. Key Points: Percolation of boninitic magmas raised the oxygen fugacity of the Troodos mantle peridotites to a limited extentThe primary boninitic magmas of the Troodos ophiolite may not be more oxidized than mid‐ocean ridge basaltsThe oxidation processes of the Troodos proto‐arc mantle may be different from those of the Izu‐Bonin‐Mariana proto‐arc mantle [ABSTRACT FROM AUTHOR]

Based on the nature of ferric sillimanite, an activity model for sillimanite containing Fe3+ is constructed, tested and adopted to calculate phase equilibria of pelitic compositions under ultrahigh‐temperature (UHT) conditions. The calculated P–T projections and pseudosections suggest that the incorporation of Fe3+ into sillimanite can fairly solve the current imperfectly topological match between thermodynamic calculations and synthetic experiments, especially at high oxygen fugacity. Fe3+ in sillimanite remarkably elevates the temperature to switch the parageneses of orthopyroxene + sillimanite (Opx + Sil) and sapphirine + quartz (Spr + Qz) in oxidized metapelites, with an increment around 50–70°C. The calculated compatibility diagrams show that the widely approbatory UHT‐diagnostic mineral assemblages of Opx + Sil and Spr + Qz usually occur in metapelites with high Mg/Fe2+ ratios, which depend on both bulk‐rock MgO and oxygen fugacity, whereas the metapelites with low Mg/Fe2+ ratios are characterized by the assemblage of Garnet + sillimanite (Grt + Sil) with or without spinel (Spl) in UHT conditions. Moreover, comprehensive comparisons suggest that the essential petrogenetic framework of natural UHT metapelites is mostly governed by the two metamorphic reactions of Opx + Sil = Spr + Grt and Grt + Sil = Spl + Spr. [ABSTRACT FROM AUTHOR]

This study presents the first complete reconstruction of gold metallurgy in Złoty Stok, Poland. The key parameters of the process (i.e., temperature of smelting and solidification, melt viscosity, oxygen fugacity) are calculated using the remnants of the process: metallurgical slags. The slags consist of silicate phases (i.e., olivine, pyroxene), sulfides and arsenides (i.e., pyrrhotite, Fe2As), as well as glass. These slags are chemically dominated by SiO2 (< 56.60 wt%), MgO (< 18.36 wt%), FeO (< 15.36 wt%), and CaO (< 15.19 wt%). The obtained results indicate that the temperature during the metallurgical process was at least 1300–1350°C, and crystallization of the slags took place until they cooled to < 1200°C. The morphology of olivine crystals in the slags indicates large differences in their cooling rate, from 5 to 300°C/h. Strongly reducing conditions during the metallurgical process (−10.5 to −11.5 log fO2) was confirmed. Low melt viscosity (logƞ = 0.26 – 0.90 Pa s) facilitated the separation of the sulfide melt rich in gold from the silicate melt being the slag precursor. The obtained results allowed existing descriptions of the smelting process in Złoty Stok to be corrected. [ABSTRACT FROM AUTHOR]

Polymer nanofibers are widely adopted in energy harvesting and pressure sensing applications owing to the large contact area and inherent compressibility. Herein, a high‐performance triboelectric nanogenerator (TENG) based on 2D siloxene‐polyvinylidene fluoride (S‐PVDF) composite nanofibrous membrane is newly evaluated. Through proper ratio optimization and facile electrospinning, the fabricated membrane shows significant improvement in dielectric property, electronegativity, and compressibility. The TENG comprising S‐PVDF membrane and Nylon 6/6 can deliver an excellent power density of 13.25 W m−2 (f ≈ 5 Hz) and easily operates low‐power electronics and Internet of things (IoTs). In addition, the excellent compressibility of membrane extends its applicability to self‐powered simultaneous detection of dynamic and static pressure, which is investigated by developing a hybrid pressure sensor (HPS) through effective integration of TENG and a capacitive pressure sensor. The HPS shows an excellent dynamic (12.062 V kPa−1 at (<3 kPa) and 2.58 V kPa−1 at (3–25 kPa)) and static (25.07 mV kPa−1 at (<3 kPa) and 5.96 mV kPa−1 at (3–25 kPa)) pressure sensitivities, respectively. Furthermore, a 2 × 2 HPS array tested and analyzed for multiple users using artificial intelligence significantly improves the accuracy (98%). Remarkable energy harvesting performance and greater accuracy of the HPS manifests better preferences for future self‐powered IoT and smart tactile‐based user authentication systems. [ABSTRACT FROM AUTHOR]

This study focuses on the nature of giant micas occurring at the contact between the Özvatan (foid‐bearing) syenites and the metamorphic basement in Central Anatolia. The studied micas are dark greenish‐black in color and crystallized within vein shape like bodies as a narrow lens. The origin and processes responsible for the formation of these independent crystals of the giant micas were investigated by mineralogical, petrographical and geochemical analyses with the use of Confocal Raman Spectroscopy (CRS), Fourier Transform Infrared (FTIR) Spectroscopy, X‐Ray Diffraction (XRD), Polarized Energy Dispersive X‐Ray Fluorescence Spectrometer (PED‐XRF) and Electron Probe Micro Analysis (EPMA). According to XRD, CRS, FTIR and EPMA data, the giant micas are phlogopite. EPMA results reveal that studied mica minerals represent the products of re‐equilibrated primary mica characterized by high MgO and FeO and low Al2O3 and TiO2 contents. The trace element concentrations of the giant micas display similar patterns with the upper crust. The giant micas are crystallized within small cubicles from an alkaline magma and their composition is possibly modified by a mixing event between the crust‐ and mantle‐derived magmas and contaminated at varying extent by the basement metamorphic rocks. [ABSTRACT FROM AUTHOR]

Crystals retain an imprint of the dynamic changes within a magma reservoir and hence contain invaluable information about the evolving conditions inside volcanic plumbing systems. However, instead of telling a single, simple story, they comprise overprinted evidence of numerous processes relating to temperature, pressure and composition that drive crystal precipitation and dissolution in magmatic systems. To decipher these different elements in the story that crystals tell, we attempt to identify the observational signatures of a simple, yet ubiquitous process: crystal precipitation and dissolution during magma cooling. To isolate this process in a complex magmatic system with intricate dynamic feedbacks, we assume that synthetic crystals precipitate and dissolve rapidly in response to deviations from thermodynamic equilibrium. In our crystalline‐scale simulations, synthetic crystals drag along the cooler‐than‐ambient melt in which they precipitated and can drive a temperature‐dependent, crystal‐driven convection. We analyze the non‐dimensional conditions for this coupled convection and record the heterogeneous thermal histories that synthetic crystals in this flow regime experience. We show that many synthetic crystals dissolve, loosing their thermal record of the convection. Based on our findings, we suggest that heterogeneity in the thermal history of crystals is more indicative of local, crystal‐scale processes than the overall, system‐wide cooling trend. Plain Language Summary: Similar to tree rings, crystals tell a story of their past through their sequential growth records. However, unlike trees, crystals are dynamic and can travel throughout the magmatic domain. We hypothesize that this mobility may result in a bias in the crystal record and prevent it from accurately recording the magma reservoir history. In order to understand what patterns natural sample crystals would record during cooling, we built a simulator that tracks individual crystals and the thermal environment they experience. We simulate how crystals drive flow, but also precipitate and dissolve in response to temperature change. Our results show that each synthetic crystal has a unique record of its past that is dependent on the temperature distribution within its vicinity. Additionally, most of the synthetic crystals dissolve in the convection, so we lose their record. Overall, the synthetic crystals in our simulation can reproduce some of the variable patterns that are often found in natural samples, suggesting that real crystals are imperfect witnesses of the magmatic dynamics they are exposed to. Key Points: Crystals in convection preserve the least information about the most dynamic flow domainCrystals in convection show signs of dissolution, suggesting a slower than actual cooling rateCrystals can record cooling, heating, and complex thermal histories even during steady cooling [ABSTRACT FROM AUTHOR]

Garnet, an important mineral component in Earth's interior, usually contains minor water as structural OH, but experimental data on OH incorporation in the mineral as a function of chemical and thermodynamic parameters remain rare. In particular, the role of oxygen fugacity (fO2) that is variable in the Earth has not been well assessed. We examine the effects of fO2 on the incorporation of OH at 1–3 GPa and 800–1000°C, by H‐annealing gem‐quality spessartine‐rich, grossular‐rich, and pyrope‐rich garnets. For each type of annealed garnet, the OH peak positions and spectral shapes are the same, suggesting the same OH incorporation mechanism(s). Under identical conditions, spessartine‐rich and grossular‐rich garnets are rich in OH, with solubility orders of magnitudes greater than for pyrope‐rich garnets. Over the studied conditions, the solubility of OH increases with pressure and temperature but decreases with fO2. The negative correlation of fO2 and OH solubility is probably due to the Fe3+ to Fe2+ reduction at more reduced conditions and the coupled OH incorporation in the structure. The effects of fO2 on OH solubility are more significant in Fe‐rich garnets. The ascertained small OH solubility in peridotite garnets, together with comparisons with relevant studies, suggest that mantle garnet is unlikely to be a major water carrier. In combination with literature‐reported positive correlation of fO2 and OH solubility in olivine, the partition coefficient of OH between garnet and olivine in the upper mantle is expected to be redox‐dependent. Plain Language Summary: The water incorporation in garnet is examined over a range of pressure, temperature, oxygen fugacity, and mineral chemistry, by conducting hydroxylation experiments with gem‐quality natural crystals. Infrared absorption bands of structural water are observed in all annealed samples, and the water solubility under otherwise identical conditions is significantly different between different types of garnets. The incorporation mechanism of water in garnet is affected by factors other than the commonly assumed hydrogarnet substitution, and appears to be influenced also by magnesium and iron in the structure. The water solubility is enhanced with decreasing oxygen fugacity, and the increase is more significant in more Fe‐rich garnets. The smaller water solubility in pyropes than previous estimates and the similarly low water storage capacity in peridotite garnets further suggest that garnet is not a major water carrier in the mantle. Key Points: An experimental study of hydroxyl incorporation in garnet over a range of pressure, temperature, oxygen fugacity, and chemical compositionThe hydroxyl solubility in garnet under otherwise identical conditions is enhanced with decreasing oxygen fugacityThe small hydroxyl storage capacity in peridotite garnet makes it unlikely a major water carrier in the mantle [ABSTRACT FROM AUTHOR]

Melt Fe3+/FeT ratios are widely used as a proxy for the oxygen fugacity (fO2) in magma systems. A particular challenge is a difficulty in quantifying the Fe2+ and Fe3+ contents, which are not easily measurable by conventional techniques. Using the Mn–Fe2+ exchange coefficient (KD) between olivine (ol) and melt (m), this study develops a novel approach to this problem using the relationship of Fem3+ ${\mathrm{Fe}}_{\mathrm{m}}^{3+}$/FemT ${\mathrm{Fe}}_{\mathrm{m}}^{\mathrm{T}}$ = 1 − KDol/mMn−Fe2+ ${\mathrm{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$ * (FeolT ${\mathrm{Fe}}_{\mathrm{ol}}^{\mathrm{T}}$/Mnol)/(FemT ${\mathrm{Fe}}_{\mathrm{m}}^{\mathrm{T}}$/Mnm). The key for applying this equation is to combine well‐defined KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$ with accurate Mn and FeT analyses of olivine and coexisting melt. The Mn and FeT analyses are readily measured by electron microprobe. To define KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$, we performed experiments at 1.0–1.75 GPa and 1250–1450°C under graphite‐buffered conditions, where FeT can be used as Fe2+ to calculate KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$. The results show that KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$ = 0.730 ± 0.025 is nearly constant over a realistic range of experimental conditions (temperature, pressure, and melt composition) relevant to basaltic magmas, allowing calculation of melt Fe3+/FeT ratios without the need for any further knowledge of these parameters. A comparison with published data, where melt Fe3+/FeT ratios have been directly measured, demonstrates that our calculation method is as accurate as Mossbauer spectroscopy and XANES techniques, thus providing a very simple and accessible approach to melt Fe3+/FeT ratio estimation. However, it should be noted that the accuracy of this method is critically reliant on: (a) accurate Mn and Fe analyses and (b) olivine‐melt chemical equilibrium. Plain Language Summary: The melt Fe3+/FeT ratios are well constrained as a function of oxygen fugacity (fO2) but difficult to measure. As nearly all Fe in olivine is Fe2+ and all Mn in olivine and basaltic melt are Mn2+, the Mn–Fe2+ exchange coefficient (KD) between olivine (ol) and melt (m) can be developed into a simple back calculation method for melt Fe3+/FeT using the formulation Fem3+ ${\mathrm{Fe}}_{\mathrm{m}}^{3+}$/FemT ${\mathrm{Fe}}_{\mathrm{m}}^{\mathrm{T}}$ = 1 − KDol/mMn−Fe2+ ${\mathrm{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$* (FeolT ${\mathrm{Fe}}_{\mathrm{ol}}^{\mathrm{T}}$/Mnol)/(FemT ${\mathrm{Fe}}_{\mathrm{m}}^{\mathrm{T}}$/Mnm). This equation only needs to know Mn and FeT contents in olivine and a coexisting melt and KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$. The former is measurable accurately by careful electron microprobe analysis. The latter is obtained here by the graphite‐buffered experiments, where FeT is used as Fe2+ to calculate KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$. We find that KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$ (0.730 ± 0.025) is close to constant over the temperature, pressure, and melt composition range relative to most basalts on Earth, which allows us to calculate the melt Fe3+/FeT ratio with the above equation, providing a simple determination of the magma fO2. This method has an accuracy comparable to more complicated and less accessible Mossbauer spectroscopy and XANES techniques. Key Points: A new oxybarometer is developed based on olivine‐melt Mn‐Fe2+ exchange coefficient (KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$)KDol/mMn−Fe2+ ${\text{KD}}_{\mathrm{ol}/\mathrm{m}}^{\mathrm{Mn}-{\mathrm{Fe}}^{2+}}$ is nearly constant with the variation of experimental conditionsThe new oxybarometer provides a simple and efficient method for melt Fe3+/FeT calculation [ABSTRACT FROM AUTHOR]

The Oman Drilling Project "Multi‐Borehole Observatory" (MBO) samples an area of active weathering of tectonically exposed peridotite. This article reviews the geology of the MBO region, summarizes recent research, and provides new data constraining ongoing alteration. Host rocks are partially to completely serpentinized, residual mantle harzburgites, and replacive. Dunites show evidence for "reactive fractionation," in which cooling, crystallizing magmas reacted with older residues of melting. Harzburgites and dunites are 65%–100% hydrated. Ferric to total iron ratios vary from 50% to 90%. In Hole BA1B, alteration extent decreases with depth. Gradients in water and core composition are correlated. Serpentine veins are intergrown with, and cut, carbonate veins with measurable 14C. Ongoing hydration is accompanied by SiO2 addition. Sulfur enrichment in Hole BA1B may result from oxidative leaching of sulfur from the upper 30 m, coupled with sulfate reduction and sulfide precipitation at 30–150 m. Oxygen fugacity deep in Holes BA3A, NSHQ14, and BA2A is fixed by the reaction 2H2O = 2H2 + O2 combined with oxidation of ferrous iron in serpentine, brucite, and olivine. fO2 deep in Holes BA1A, BA1D, and BA4A is 3–4 log units above the H2O‐H2 limit, controlled by equilibria involving serpentine and brucite. Variations in alteration are correlated with texture, with reduced, low SiO2 assemblages in mesh cores recording very low water/rock ratios, juxtaposed with adjacent veins recording much higher ratios. The proportion of reduced mesh cores versus oxidized veins increases with depth, and the difference in fO2 recorded in cores and veins decreases with depth. Plain Language Summary: The Oman Drilling Project developed a "Multi‐Borehole Observatory" (MBO) in an area of active weathering of tectonically exposed peridotite, to study the geochemistry, mechanics, and hydrology of peridotite alteration, which modifies the mineralogy, composition, density, and rheology of mantle lithologies, creates and sustains plate boundaries, and forms dramatic redox gradients. In turn, these redox conditions support a unique subsurface microbial ecosystem, form free H2 gas, facilitate methane generation, and potentially play a role in the origin of life on this and other planets. This paper provides an overview of the geology of the area within and surrounding the MBO, a summary of recent research on core and fluids from three new cored boreholes and four new rotary boreholes in the MBO, together with older Omani water monitoring well NSHQ14, and new data and calculations constraining ongoing peridotite alteration in this area. We constrain the igneous history of the mantle rocks, the extent to which they have been hydrated, carbonated, and oxidized. Highlights include new hypotheses on mechanisms of shallow sulfur depletion and deeper enrichment, and new insights into the interaction of water and minerals that controls the partial pressures of oxygen and hydrogen in this important geochemical environment. Key Points: Ongoing alteration decreases in intensity with increasing depth below the present erosional surfaceSulfur is accumulating in a supergene enrichment zone from 30 to 150 m below the present erosional surfaceDeep oxygen fugacity is fixed by H2 gas saturation = plus ongoing oxidation of Fe2+ in three holes and serpentine‐brucite equilibria in four holes [ABSTRACT FROM AUTHOR]

Dichlorodiphenyldichlorethane (1,1,1‐trichloro‐2,2‐bis(p‐chlorophenyl)ethane) (DDT) is an organochlorine insecticide that was widely used from the late 1940s to the 1970s in fruit orchards in the Okanagan valley, British Columbia, Canada, and in the process, contaminated American robin (Turdus migratorius) food chains with the parent compound and metabolite dichlorodiphenyldichloroethylene (1,1‐dichloro‐2,2‐bis(4‐chlorophenyl)ethylene) (p,p′‐DDE). In the present study, we examined the biological fate of these DDT‐related (DDT‐r) compounds at the same sites/region 26 years after a previous study by: (1) collecting soil, earthworms, and American robin eggs from apple, cherry, and pear orchards; (2) characterizing the diet and trophic positions of our biota using stable isotope analyses of δ13C and δ15N; and (3) estimating fugacity, biota‐soil‐accumulation factors (BSAFs), and biomagnification factors (BMFs). Mean p,p′‐DDE concentrations (soil: 16.1 µg/g organic carbon‐lipid equivalent; earthworms: 96.5 µg/g lipid equivalent; eggs: 568 µg/g lipid equivalent) revealed that contamination is present at elevated levels similar to the 1990s and our average soil DDE:DDT ratio of 1.42 confirmed that DDT is slowly degrading. American robins appeared to feed at similar trophic levels, but on different earthworms as indicated by egg stable isotope values (mean δ15N = 8.51‰ ± 0.25; δ13C = −26.32‰ ± 0.12). Lumbricidae and Aporrectodea worms shared a roughly similar δ15N value; however, Lumbricus terrestris showed a markedly enriched δ13C isotope, suggesting differences in organic matter consumption and physiological bioavailability. Biota‐soil‐accumulation factors and BMFs ranged over several orders of magnitude and were generally >1 and our fugacity analyses suggested that p,p′‐DDE is still thermodynamically biomagnifying in American robin food chains. Our results demonstrate that DDT‐r in fruit orchards remains bioavailable to free‐living terrestrial passerines and may pose a potential toxicological risk. Environ Toxicol Chem 2021;40:3379–3391. © 2021 Her Majesty the Queen in Right of Canada. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada. [ABSTRACT FROM AUTHOR]

Late Mesozoic extensional mechanisms in the Great Xing'an Range (GXR) and relevant crust–mantle interactions are complicated, which result in widespread magmatisms with diverse parental origins and petrogenesises. In this paper, we present the lithology, whole‐rock geochemistry, and zircon U–Pb–Lu–Hf isotopes for granodiorite‐monzogranite rocks (GM) and their enclaves of quartz monzodiorites in the Zhalantun area, east of central GXR. Zircon U–Pb dating results reveal that both GM rocks and their enclaves of quartz monzodiorites yield a nearly identical crystallization age of ~125 Ma. The GM rocks exhibit weak peraluminous and high‐K calc‐alkaline compositions with high SiO2, Na2O + K2O, and Al2O3 contents, and low MgO, Mg#, Fe2O3T, and TiO2 contents, which are characterized by fractionated REE patterns, relatively strong negative Eu anomalies, enrichments of LILEs (e.g., Rb, Ba, and K), and depletions of Nb, Ta, P, and Ti. The parental origins for GM samples were juvenile crustal materials, with positive zircon εHf(t) values of +2.5 to +12.9. The whole‐rock and zircon geochemical simulations limit slightly lower GM magma crystallization temperatures (TTi‐Zrn) of 683–824°C and relatively more oxidizing conditions (log(fO2) = FMQ+7.6–FMQ‐6.8), and further confine that they were probably formed by ~10–35% degrees of fluid‐present partial melting of lower to middle crustal materials, with fractional crystallization and/or residual mineral phases of plagioclase, amphibole, clinopyroxene, and garnet. By contrast, the enclaves of quartz monzodiorites possess lower SiO2 and Na2O + K2O compositions, but higher MgO, Mg#, Fe2O3T, and TiO2 values, which are consistent with metaluminous–weak peraluminous and high‐K calc‐alkaline series. All quartz monzodiorites exhibit sub‐parallel right‐declined REE patterns, negligible to none Eu anomalies, enrichments of LILEs, and depletions of Nb, Ta, and Ti. Combined with mineral morphology and disequilibrium structures, the whole‐rock geochemical and Hf isotopic simulations imply that parental magmas for quartz monzodiorites were hybrid mixtures between ~50% host GM acid magmas and ~50% ancient crust compositions, with a wide range of zircon εHf(t) of +14.0 to −7.7, slightly higher TTi‐Zrn of 710–835°C, and lower log(fO2) of FMQ+8.2–FMQ‐10.5. Taken together, felsic plutons in the Zhalantun area correspond to an episode of extensional mechanism‐related crust–mantle interactions, which might be induced by either the Mongol‐Okhotsk domain or Palaeo‐Pacific tectonic domain, or both of them. [ABSTRACT FROM AUTHOR]

The equation of state (EOS) for plasmas of the two lightest elements H and He, and mixtures as typical for the plasmas in the sun are calculated. The contributions of deep bound states are included by using inverted fugacity expansions. The inversion of fugacities to densities is reduced to solvable algebraic problems and expressed by rational polynomials. The calculation of relative pressures is carried out separately for low and high densities. Near the crossing point, in between, the separate solutions are connected to each other by smooth concatenation. Applications to hydrogen–helium plasmas in the sun including estimates for the isentropic EOS are discussed. [ABSTRACT FROM AUTHOR]

The Raman spectral behavior of N2, CO2, and CH4 in ternary N2–CO2–CH4 mixtures was studied from 22°C to 200°C and 10 to 500 bars. The peak position of N2 in all mixtures is located at lower wavenumbers compared with pure N2 at the same pressure (P)–temperature (T) (PT) conditions. The Fermi diad splitting in CO2 is greater in the pure system than in the mixtures, and the Fermi diad splitting increases in the mixtures as CO2 concentration increases at constant P and T. The peak position of CH4 in the mixtures is shifted to higher wavenumbers compared with pure CH4 at the same PT conditions. However, the relationship between peak position and CH4 mole fraction is more complicated compared with the trends observed with N2 and CO2. The relative order of the peak position isotherms of CH4 and N2 in the mixtures in pressure–peak position space mimics trends in the molar volume of the mixtures in pressure–molar volume space. Relationships between the direction of peak shift of individual components in the mixtures, the relative molar volumes of the mixtures, and the attraction and repulsion forces between molecules are developed. Additionally, the relationship between the peak position of N2 in ternary N2–CO2–CH4 mixtures with pressure is extended to other N2‐bearing systems to assess similarities in the Raman spectral behavior of N2 in various systems. [ABSTRACT FROM AUTHOR]

The Jiudingshan Cu–Mo deposit is spatially and temporally associated with potassic granitic intrusions (monzogranitic porphyry and porphyritic‐like granite) in a post‐collisional intracontinental setting in Western Yangtze Craton, Western Yunnan, China. Zircon U–Pb dating for granitoids yields the crystallization age of 34.2–35.1 Ma, and that of lamprophyre and diabase is ca. 35 Ma as well. Whole‐rock geochemical data suggest that the granitoids belong to high‐K calc‐alkaline or shoshonite series, and are characterized by enrichment of K, Rb, U, and Th, and depletion ofSr, Ba, Nb, Ta, Ti, and P. The lamprophyre is characterized by high‐K (K2O/Na2O = 3–5), belonging to shoshonite series, and the diabase contains lower K (K2O/Na2O < 0.5), belonging to calc‐alkaline series. A few mafic rock samples have significantly higher REE contents than the granite counterparts. Geochemistry results indicate that the mafic intrusions are not the source of granitic intrusions. Combined with published isotope data, we conclude that the granitic intrusions were most likely originated from partial melting of a Neoproterozoic intra‐crustal amphibolitic source, but mixed with a mantle‐derived component; while the mafic intrusions were originated from partial melting of an EM II mantle source. Felsic magmas from dual sources of crust and mantle could provide Mo and Cu for mineralization, respectively. Trace element analysis of zircons shows that the initial magmas had high oxygen fugacity, which is favourable for the migration of Cu and Mo. Moreover, it can be recognized from the whole‐rock major and trace element data that a relatively weak fractionation occurred during magmatic evolution, which made Mo enriched to a certain extent and at the same time, part of Cu remained in the melt, eventually forming the Jiudingshan Cu–Mo system. [ABSTRACT FROM AUTHOR]

The article presents a design of the mantle transects in Africa using the PTXFO2 diagrams and according to data of mantle xenocrysts and diamond inclusions. Topics covered include the construction of the diagrams using analyses of garnets, eclogitic minerals and inclusions in diamonds in open publications, the reason behind the irregular distribution of eclogites in kimberlite pipes and abundance in Roberts Victor, and the metasomatic processes in the mantle of Luaxe and Cuilo pipes.

We investigated the electrical conductivity of Ti‐H‐doped synthetic olivine aggregates at 4 GPa, 873–1273 K, and controlled oxygen fugacities. Under a given pressure and temperature, electrical conductivity depends on both hydrogen and Ti content, but these samples show different conductivity behavior from that observed in Ti‐poor sample such as San Carlos olivine. We found that when Ti content is comparable to or larger than hydrogen content, Ti has notable effects on electrical conductivity, but the effects of Ti is different between the H‐rich and the H‐poor regimes. In the H‐rich regime, electrical conductivity of olivine is weakly dependent on Ti content but has different sensitivity to water content than a Ti‐poor olivine. In contrast, in the H‐poor regime, electrical conductivity of Ti‐rich olivine is substantially higher than the conductivity of Ti‐poor olivine. As a consequence, the effect of hydrogen for the Ti‐rich synthetic olivine on electrical conductivity is smaller than for the Ti‐poor (natural) olivine for the modest H content expected in the asthenosphere, whereas in the H‐poor lithosphere Ti will enhance the electrical conductivity substantially. Possible models to explain these observations are proposed including the interaction of Ti‐related defects and H‐related defects as well as the charge transfer caused by the hopping conduction due to Ti3+ ⇔ Ti4+ under the H‐poor conditions. We conclude that the addition of Ti to olivine affects the behavior of H‐related defects, and therefore the applications of results from Ti‐rich olivine samples to the Ti‐poor real Earth need to be made with great care. Key Points: Ti has a strong effect on electrical conductivity of sample; however, its influence is completely different in H‐rich and H‐poor regimesDefect models to explain these observations are proposed by interaction of Ti‐related and H‐related defects and hopping of small polaronIt is suggested that the applications of results from Ti‐rich olivine samples to the Ti‐poor real Earth need to be made with great care [ABSTRACT FROM AUTHOR]

Temperature and fluid content are critical parameters that control rock rheology and strain localization in the continental crust. Here, we determine by thermodynamic modelling the T‐MH2O of localized ductile shearing during cooling of three different granitoid plutons: the Rieserferner and the Adamello plutons in the Italian Alps, and the Lake Edison pluton in the Sierra Nevada—USA. Shear zones exploited precursor joints, associated veins and alteration zones. T‐MH2O and P−T phase diagram sections were computed with Perple_X in the system MnO−Na2O−CaO −K2O−FeO−MgO−Al2O3−SiO2−H2O−Fe2O3. The phase diagram sections show that the nucleation of the brittle precursors (joints, veins) occurred at T» 450°C at fluid‐saturated conditions. Localized ductile shearing likely occurred at temperature ranging between 420 and 460°C evolving from initially fluid‐saturated to fluid‐undersaturated conditions in a closed system. In this temperature range, granitoid rocks are potentially subject to a series of retrograde metamorphic reactions replacing the load‐bearing feldspars with weaker phyllosilicates. Metamorphic reactions occurred in spatial association with the precursory structures, leading to localized shearing. Decreasing temperature and fluid‐undersaturated conditions likely hampered progressive strain accommodation in shear zones by slowing down metamorphic reactions, thermally activated dislocation creep processes, fluid‐mediated deformation mechanisms and weakening mechanisms. Polyphase granitoid ultramylonite and mylonitic quartz veins have been affected differently by the fluid‐undersaturated conditions of the system, as consequence of different dominant deformation mechanisms and syn‐kinematic paragenesis during localized shearing. Localized ductile shearing in cooling plutons effectively occurs in a limited temperature range (420–460°C) in which the strain accommodation capacity of the shear zone is controlled by the negative feedback between the cooling rate, the kinetics of metamorphic reactions and deformation mechanisms, and the consumption of the limited amount of available fluids. [ABSTRACT FROM AUTHOR]

Porphyry deposits occur not only in subduction zones, but also in collisional belts worldwide. The magmatic oxygen fugacity (ƒo2) is an important element for the formation of porphyry, and influences the processes in source, migration, and precipitation of Cu and other chalcophile elements. Magmatic sulphur exists mainly as sulphate (SO42−) at higher oxygen fugacity, which combines with chalcophile elements (e.g., Cu, Au) as ion complexes then formed the ore‐bearing magma. In contrast, magmatic sulphur exists mainly as sulphide (S2−), sulphide will precipitate easily. A magmatic event usually involves multiple intrusive activities. These porphyries have various ƒo2 evolutions, implying that they are formed in different formation environments or dynamic mechanisms. In a subduction setting, plates begin to dehydrate and then partial melting occurs in the early stage of subduction. Following the extensive dehydration, partial melting occurs as the plate diving deeper. As a result, the later magma is more oxidative than the earlier one. While under the collisional setting, porphyritic magma is likely related to the previous arc magmatism of subduction or juvenile mantle components in the thickened lower crust. The hydrous and metalliferous fertile magma formed. Then, reduction of water supply is the possible factor that leads to the gradually decrease of ƒo2. As a result of this study, metallogenic elements are usually developed in later porphyritic magma at a subduction environment, but in the early porphyritic magma at a collisional environment. This can provide guidance for prospecting of porphyry deposits in multi‐phases of porphyritic magma districts. [ABSTRACT FROM AUTHOR]

An aerodynamic conical nozzle levitator (CNL) has been used to measure the melting temperatures of refractory ceramics. The well‐established method of cooling traces has been adapted to allow measurements for air‐sensitive samples using a controlled atmosphere, where the oxygen partial pressure can be adjusted and monitored in real time. In this study, we explain the details of a system that we developed for use at the Spallation Neutron Source (Oak Ridge National Laboratory). Measurements of the melting behavior of (Fe,Cr,Al)3O4 spinels were made between log (PO2 (atm)) of −0.7 and −5. The melting temperature of hercynite is found to be oxygen potential dependent, ranging between 1692 and 1767°C at log (PO2) values from −4.42 to −0.70. [ABSTRACT FROM AUTHOR]

The Shihu quartz vein‐type gold deposit, the largest gold deposit in the central North China Craton, occurs within wall rocks of Neoarchean TTG (tonalite–trondhjemite–granodiorite) gneiss and shows a close relationship with the early Cretaceous Mapeng granitoid pluton and various intermediate–mafic dykes. The occurrence, morphology, composition, and precipitation mechanism of the Au–Ag minerals are short of research, which is the purpose of this study. The primary mineral assemblage of orebody contains quartz, calcite, and base‐metal sulphides including pyrite, galena, sphalerite, chalcopyrite, and minor pyrrhotite and enargite. The Au–Ag minerals can be classified into three distinct types, namely, (a) quartz‐hosted, (b) pyrite‐hosted, and (c) base‐metal sulphidehosted, corresponding to formation sequence. Electron microprobe analysis indicates that these Au–Ag minerals show fineness (=Au/[Au + Ag] × 1,000) ranging from 976 to 366 with an average of 667 and are rich in Bi, Te, and Hg while deficient of Cu, As, and Se. Bismuth and tellurium in the Au–Ag minerals show a linear relationship with Au, whereas in the coexisted sulphides are almost below detection limits. We suggest that Bi and Te fundamentally influenced the transportation, enrichment, and precipitation of gold as scavengers to concentrate and deposit gold at the location with an "appropriate distance" from magma. Phase analyses of native bismuth and Bi–Te minerals included in pyrite, reported for the first time in Shihu Gold deposit, imply that the gold precipitation witnessed the ore‐forming fluid evolution with log fTe2 decreasing from approximately −11 to approximately −15 and log fS2 increasing from approximately −13 to more than −11. Mineralogical mapping with the fineness of Au–Ag minerals (fineness contours) suggest that the ore‐forming fluids came from the deep earth beneath the north of the mining area with excellent gold potential, which has been verified by later drilling. [ABSTRACT FROM AUTHOR]

One atmosphere experimental studies have been conducted on two amygdule‐free representative samples from Khandwa, Madhya Pradesh, Central India, belonging to Eastern Deccan Volcanic province in order to understand mineral petrogenesis, crystallization history of the parent magma and role of liquid immiscibility. One atm experiments were carried out on these two samples at specified temperatures on designated time in order to understand crystallization history. The run products were identified both by optical means and electron microprobe analysis. The identified run products include pyroxenes, feldspar, opaques phase (oxide and sulphide), silica phases, and glass (both brown and colourless variety). The run product pyroxenes belong to quadrilateral pyroxene, and species‐wise correspond to augite, clinoenstatite, and pigeonite. Feldspars in majority are found to be anorthoclase (which are interpreted to have been formed during sudden crystallization in contact with water at shallow depth during experiments) and less commonly calcic plagioclase (in the range of labradorite to anorthite). Opaque phases have both oxide and sulphide, namely hematite, magnetite, martite, and pyrite, respectively. The zoned nature between the oxide and sulphide phases is suggestive of oscillation of oxygen fugacity during crystallization. The run product silica phase corresponds to tridymite. The silica‐rich glass (colourless) is overwhelmingly dominant, whereas silica‐poor glass (brown glass) is a manifestation of liquid immiscibility. The silica‐rich glasses give rise to direct crystallization of tridymite, whereas silica‐poor glasses act as the main driving liquid (or parent liquid) to further the crystallization towards lower temperature. The crystallization behaviour of the parent magma, and liquid immiscibility can be well documented with reference to forsterite‐silica phase diagram; in this phase diagram, the parent liquid corresponds to normative Qtz: 2.542, Fo: 0.098, and En: 0.34. The ambient parent liquid plots very close to Ab apex with reference to the Di‐Ab‐An phase diagram. The clear and distinct zonation pattern present in the opaque phases signifies that crystallization straddles between both oxidizing and reducing condition yielding crystallization of both oxide and sulphide phases. Our study indicates a unique role of liquid immiscibility of the parent magma supplemented by oscillation of oxidizing and reducing conditions giving rise to ensemble of variety of glass compositions, silicate, and opaque phases. [ABSTRACT FROM AUTHOR]

Recent studies have revealed that Earth's deep mantle may have a wider range of oxygen fugacities than previously thought. Such a large heterogeneity might be caused by material subducted into the deep mantle. However, high‐pressure phase relations are poorly known in systems including Fe3+ at the top of the lower mantle, where the subducted slab may be stagnant. We therefore conducted high‐pressure and high‐temperature experiments using a multi‐anvil apparatus to study the phase relations in a Fe3+‐bearing system at 26 GPa and 1573–2073 K, at conditions prevailing at the top of the lower mantle. At temperatures below 1923 K, MgSiO3‐rich bridgmanite, an Fe3+‐rich oxide phase, and SiO2 coexist in the recovered sample. Quenched partial melt was observed above 1973 K, which is significantly lower than the solidus temperature of an equivalent Fe3+‐free bulk composition. The partial melt obtained from the Fe3+‐rich bulk composition has a higher iron content than coexisting bridgmanite, similar to the Fe2+‐dominant system. The results suggest that strong mantle oxygen fugacity anomalies might alter the subsolidus and melting phase relations under lower mantle conditions. We conclude that (1) a small amount of melt may be generated from an Al‐depleted region of a stagnant slab, such as subducted former banded‐iron‐formation, and (2) Fe3+ is not transported into the deep part of the lower mantle because of its incompatibility during melting. Key Points: We determined phase relationships of Fe3+‐rich system at top of the lower mantleMelting temperature of Fe3+‐rich system is lower than Fe2+‐dominant systemFe3+ may not be transported into the deep lower mantle because of its incompatibility [ABSTRACT FROM AUTHOR]

The investigated area around Sarvapuram represents a part of the Karimnagar granulite terrane of the Eastern Dharwar Craton, India. Garnet–bearing gneiss is hosted as enclaves, pods within granite gneiss and charnockite. It is largely made up of garnet, orthopyroxene, cordierite, biotite, plagioclase, K–feldspar, sillimanite and quartz. The peak metamorphic stage is represented by the equilibrium mineral assemblage i.e. garnet, orthopyroxene, cordierite, biotite, plagioclase, sillimanite and quartz. Breakdown of the garnet as well as preservation of the orthopyroxene–cordierite symplectite, formation of cordierite with the consumption of the garnet + sillimanite + quartz represents the decompressional event. The thermobarometric calculations suggest a retrograde P–T path with a substantial decompression of c. 3.0 kbar. The water activity (XH2O) conditions obtained with the winTWQ program for core and symplectite compositions from garnet–bearing gneiss are 0.07–0.14 and 0.11–0.16 respectively. The quantitative estimation of oxygen fugacity in garnet–bearing gneiss reveal log fO2 values ranging from −11.38 to −14.05. This high oxidation state could be one of the reasons that account for the absence of graphite in these rocks. [ABSTRACT FROM AUTHOR]

The nature of lattice‐preferred orientation (LPO) in olivine‐rich rocks strongly influences many important physical properties of Earth's upper mantle. Different LPO types have been observed to develop in deformation experiments on olivine‐rich rocks carried out at different water fugacity conditions. The development of the different LPO types has been attributed to dislocation slip systems in olivine having different sensitivities to water fugacity, but this hypothesis has not been directly tested. To measure the influence of water fugacity on the relative strengths of olivine dislocation slip systems, we carried out a series of deformation experiments on olivine single crystals under either anhydrous or hydrous conditions. The crystals were oriented to activate either the (010)[100], (001)[100], or (100)[001] dislocation slip systems using a direct shear geometry, which allows for isolation of single slip systems, in contrast to the multiple systems activated in experiments carried out in compression. Post‐deformation electron backscatter diffraction analyses reveal orientation gradients consistent with deformation occurring via the motion of dislocations on the activated slip systems. Crystals in all of the investigated orientations exhibit hydrolytic weakening, but crystals oriented to activate the (001)[100] slip system exhibit the largest degree of weakening. These results are consistent with a water‐induced change in LPO in olivine‐rich rocks deforming by dislocation creep. The rheological data obtained from the experiments can be used to improve models of LPO evolution in Earth's mantle, which is critical for imaging the structure of Earth's interior and predicting the movement of Earth's tectonic plates. Key Points: All investigated olivine dislocation slip systems exhibit hydrolytic weakeningThe strength of the (001)[100] slip system is most sensitive to water fugacityThe different sensitivities of slip systems to water fugacity may explain the different LPO types observed in mantle rocks [ABSTRACT FROM AUTHOR]

An accurate flow law for dislocation creep of quartz aggregates is critical for the understanding of continental rheology, numerical modeling of lithospheric processes, and the interpretation of microstructures of natural quartz‐bearing mylonites. Despite many decades of research, considerable discrepancies still exist among quartz flow laws determined from different experiments. We demonstrate that the key to reconcile these discrepancies is to consider the pressure dependence of the activation enthalpy. From existing high‐quality creep experiments on quartz aggregates, we critically identified test runs having microstructures and stress‐strain curves indicating steady state regimes 2 and 3 dislocation creep and used the data to obtain a set of flow law parameters most consistent among existing experiments. Because estimates of strain rate and stress from natural mylonites are bound with large uncertainties, they cannot be used to construct a flow law better than one determined from well‐controlled creep experiments. A large number of geological studies and modern GPS observations suggest that crustal scale ductile shear zones likely flow at a strain rate range between 10−13 and 10−11 s−1. In this strain rate range, our flow law predicts flow stresses broadly consistent with stress estimates from many natural mylonites based on well‐calibrated piezometers for dynamically recrystallized quartz grains. Key Points: Pressure dependence of activation enthalpy is key to reconcile discrepancies among flow laws for quartz derived from different experimentsA consistent flow law for climb‐accommodated dislocation creep for quartzite is obtained from critically selected high‐quality experimental dataThe new flow law is discussed in the context of stress estimates from natural mylonites based on various piezometric methods [ABSTRACT FROM AUTHOR]

The transition between antigorite‐serpentinite and chlorite‐harzburgite at Cerro del Almirez (Betic Cordillera, Southern Spain) exceptionally marks in the field the front of antigorite breakdown at high pressure (~16–19 kbar) and temperature (~650°C) in a paleosubducted serpentinite. These ultramafic lithologies enclose three types of metarodingite boudins of variable size surrounded by metasomatic reaction rims. Type 1 Grandite‐metarodingite (garnet+chlorite+diopside+titanite±magnetite±ilmenite) mainly crops out in the antigorite‐serpentinite domain and has three generations of garnet. Grossular‐rich Grt‐1 formed during rodingitization at the seafloor (<2 kbar, ~150–325°C, ~FMQ buffer). During subduction, the alternating growth of Grt‐2b (richer in andradite and pyralspite components than Grt‐1) and Grt‐3 (very rich in andradite component) reflects the change from internally buffered metamorphic conditions (>10 kbar, ~350–650°C, ~FMQ buffer) to influx events of oxidizing fluids (fO2 ~HM buffer) released by brucite breakdown in the host antigorite‐serpentinite. Type 2 Epidote‐metarodingite (epidote+diopside+titanite±garnet) derives from Type 1 and is the most abundant metarodingite type enclosed in dehydrated chlorite‐harzburgite. Type 2 formed by increasing μSiO2 (from −884 to −860 kJ/mol) and decreasing μCaO (from −708 to −725 kJ/mol) triggered by the flux of high amounts of oxidizing fluids during the high‐P antigorite breakdown in serpentinite. The growth of Grt‐4, with low‐grandite and high‐pyralspite components, in Type 2 metarodingite accounts for progressive reequilibration of garnet with changing intensive variables. Type 3 Pyralspite‐metarodingite (garnet+epidote+amphibole+chlorite±diopside+rutile) crops out in the chlorite‐harzburgite domain and formed at peak metamorphic conditions (16–19 kbar, 660–684°C) from Type 2 metarodingite. This transformation caused the growth of a last generation of pyralspite‐rich garnet (Grt‐5) and the recrystallization of diopside into tremolitic amphibole at decreasing fO2 and μCaO (from −726 to −735 kJ/mol) and increasing μMgO (from −630 to −626 kJ/mol) due to chemical mixing between the metarodingite and the reaction rims. The different bulk Fe3+/FeTotal ratios of antigorite‐serpentinite and chlorite‐harzburgite, and of the three metarodingite types, reflect the highly heterogeneous oxidation state of the subducting slab and likely point to the transfer of localized oxidized reservoirs, such as metarodingites, into the deep mantle. [ABSTRACT FROM AUTHOR]

Abstract: To estimate the dissociation conditions of semiclathrate hydrates in gas + tetra‐n‐butyl ammonium halide aqueous solution systems, we introduce an extended thermodynamic framework, which was originally proposed by Javanmardi and colleagues for modeling of gas hydrate dissociation conditions in aqueous solutions of electrolytes (12 [1998] 219–222, Energy and Fuels). For evaluating the hydrate dissociation conditions, we apply the van der Waals–Platteuw theory. In addition, we incorporate the Peng–Robinson equation of state and the activity coefficient model of Pitzer and Mayorga to respectively calculate gas/vapor fugacity and tetra‐n‐butyl ammonium halide activity coefficient. Using this model, we have estimated the semiclathrate hydrate dissociation conditions in the systems of CH4, N2, or CO2 + tetra‐n‐butylammonium bromide + water; CO2 + tetra‐n‐butylammonium fluoride + water; and CH4 or CO2 + tetra‐n‐butylammonium chloride + water systems. The model results are found in satisfactory agreement with the selected experimental data collected from literature. Also, the average absolute temperature deviations for the studied systems are about 0.3 K. [ABSTRACT FROM AUTHOR]

Abstract: Raman spectroscopy yields information about the internal vibrational modes of covalently bonded molecules, which are sensitive to the local molecular environment. As such, Raman spectra of a gas composed of covalently bonded molecules collected at different temperatures and/or pressures show variations in band positions and other spectral features, reflecting molecular‐scale interactions (attraction and repulsion) among gas particles associated with the local physical and chemical environment. Because the molecules interact, gases are nonideal, and fugacity is the fundamental thermodynamic quantity that describes partial pressures of gases, adjusted to account for the nonideality. The fugacity of a substance is generally obtained from thermodynamic calculations rather than by direct analysis or measurement and, as such, is conceptually nebulous. Here, we perform spectroscopic analyses of a gas mixture of known composition at variable and known pressures and couple these results with thermodynamic calculations of gas fugacities. We show that Raman peak shifts in gas mixtures are directly correlated to fugacities of the component gas species. Our results thus provide experimental evidence that fugacities of gases can be estimated from Raman spectra collected in situ. By this approach, the thermodynamic quantities fugacity and the related thermodynamic property activity are linked directly with underlying molecular‐scale phenomena, according to the vibrational properties of molecular species. This represents a tractable method to efficiently obtain large datasets on thermodynamic properties of gas mixtures, and with some adjustments, may lead to a viable method for developing nonideal mixing rules for other substances, such as crystalline solid solutions, aqueous ions, and electrolytes. [ABSTRACT FROM AUTHOR]

Oxidative thermal removal of the polymeric templates is not trivial for molybdenum oxides and hampers mesostructuring of this material. At ambient oxygen fugacity, MoVI is the thermodynamically stable oxidation state and sublimation of MoO3 leads to a quick loss of the mesostructure through Oswald ripening. Taking advantage of the Boudouard equilibrium allows to fix the oxygen fugacity at a level where non-volatile MoO2− x is stable while carbonaceous material may be oxidized by CO2. Mesostructured MoO2− x can be chemically converted into MoO3 or MoN under retention of the mesostructure. [ABSTRACT FROM AUTHOR]

High-temperature solid-state electrochemistry techniques (EMF method) were used to measure the oxygen fugacity ( fO2) of the ordinary chondrites Ochansk (H4), Savtschenskoje (LL4), Elenovka (L5), Vengerovo (H5), and Kharkov (L6). The fO2 results are presented in the form of the following equations: [ABSTRACT FROM AUTHOR]

Mantle convection and large-scale plate motion depend critically on the nature of the lithosphere-asthenosphere boundary and thus on the viscosity structure of Earth's upper mantle, which is determined by the rheological properties of its constituent minerals. To constrain the flow behavior of orthopyroxene, the second most abundant constituent of the upper mantle, deformation experiments were carried out in triaxial compressive creep on fine-grained (~6 μm) samples of enstatite at high pressures (3.8-6.3 GPa) and high temperatures (1323-1573 K) using a deformation-DIA apparatus. Based on results from this study, the deformation behavior of enstatite is quantitatively presented in the form of a flow law that describes the dependence of deformation rate on differential stress, water fugacity, temperature, and pressure. Specifically, the creep rate depends approximately linearly on stress, indicating deformation in the diffusion creep regime. A least squares regression fit to our data yielded a flow law for diffusion creep with an activation energy of ~200 kJ/mol and an activation volume of ~14 × 10−6 m3/mol. The magnitude of the water-weakening effect is similar to that for olivine with a water fugacity exponent of r ≈ 0.7. This strong dependence of viscosity on water fugacity (concentration) indicates that the viscosity of an orthopyroxene-bearing mantle varies from one geological setting to another, depending on the large-scale water distribution. Based on the rheology contrast between olivine and enstatite, we conclude that olivine is weaker than enstatite throughout most of the upper mantle except in some shallow regions in the diffusion creep regime. [ABSTRACT FROM AUTHOR]

We theoretically derived flow laws for quartz dislocation creep using climb-controlled dislocation creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen-bearing species along different crystallographic axes (// c, ⊥ R, and ⊥ c) of α-quartz and β-quartz, and pipe diffusion of H2O, to be the elementary processes of dislocation climb. The relationships between differential stress ( σ) and strain rate ( [ABSTRACT FROM AUTHOR]

Mineral inventories of enstatite chondrites; ( EH and EL) are strictly dictated by combined parameters mainly very low dual oxygen ( fO2) and sulfur ( fS2) fugacities. They are best preserved in the Almahata Sitta MS-17, MS-177 fragments, and the ALHA 77295 and MAC 88136 Antarctic meteorites. These conditions induce a stark change of the geochemical behavior of nominally lithophile elements to chalcophile or even siderophile and changes in the elemental partitioning thus leading to formation of unusual mineral assemblages with high abundance of exotic sulfide species and enrichment in the metallic alloys, for example, silicides and phosphides. Origin and mode of formation of these exotic chondrites, and their parental source regions could be best scrutinized by multitask research experiments of the most primitive members covering mineralogical, petrological, cosmochemical, and indispensably short-lived isotopic chronology. The magnitude of temperature and pressure prevailed during their formation in their source regions could eventually be reasonably estimated: pre- and postaccretionary could eventually be deduced. The dual low fugacities are regulated by the carbon to oxygen ratios estimated to be >0.83 and <1.03. These parameters not only induce unusual geochemical behavior of the elements inverting many nominally lithophile elements to chalcophile or even siderophile or anthracophile. Structure and mineral inventories in EL3 and EH3 chondrites are fundamentally different. Yet EH3 and EL3 members store crucial information relevant to eventual source regions and importantly possible variation in C/O ratio in the course of their evolution. EL3 and EH3 chondrites contain trichotomous lithologies (1) chondrules and their fragments, (2) polygonal enstatite-dominated objects, and (3) multiphase metal-rich nodules. Mineralogical and cosmochemical inventories of lithologies in the same EL3 indicate not only similarities ( REE inventory and anomalies in oldhamite) but also distinct differences (sinoite-enstatite-graphite relationship). Oldhamite in chondrules and polygonal fragments in EL3 depict negative Eu anomaly attesting a common cosmochemical source. Metal-dominated nodules in both EL3 and EH3 are conglomerates of metal clasts and sulfide fragments in EH3 and concentrically zoned C-bearing metal micropebbles (≥25 μm ≤50 μm) in EL3 thus manifesting a frozen in unique primordial accretionary metal texture and composition. Sinoite-enstatite-diopside-graphite textures reveal a nucleation and growth strongly suggestive of fluctuating C/O ratio during their nucleation and growth in the source regions. Mineral inventories, sulfide phase relations, sinoite-enstatite-graphite intergrowth, carbon and nitrogen isotopic compositions of graphite, spatial nitrogen abundance in graphite in metal nodules, and last but not least 129I/129Xe and 53Mn/53Cr systematics negate any previously suggested melting episode, pre-accretionary or dynamic, in parental asteroids. [ABSTRACT FROM AUTHOR]

Fluid inclusions in the metamorphic aureole of the Eureka Valley-Joshua Flat-Beer Creek ( EJB) pluton in the White-Inyo Range, California, reveal the compositions and origin of fluids that were present during variable recrystallization of quartzite with sedimentary grain shapes to metaquartzite with granoblastic texture. Metamorphosed sedimentary formations, including quartzites, marbles, calcsilicates and schists, became ductile and strongly attenuated in the aureole during growth of the magma chamber. The microstructures of quartzites have an unusual distribution in that within ~250 m from the pluton, where temperatures exceeded 650 °C, they exhibit relict sedimentary grain shapes, only small amount of grain boundary migration ( GBM), and crystallographic preferred orientations ( CPOs) dominated by slip. At distances >250 m, quartzites were completely recrystallized by GBM and CPOs are indicative of prism [c] slip, characteristics that are typically associated with H2O-assisted, high- T recrystallization. The lack of extensive GBM in the inner aureole can be attributed to rapid replacement of H2O by CO2 produced by reaction of quartz grains with calcite cement that also produced interstitial wollastonite. Fluid inclusions in the inner aureole generally occur in margins of quartz grains and are either wholly aqueous (Type 1) or also contain H2S, CO2 and CH4 (Type 2). Type 2 inclusions occur only in some stratigraphic layers. In both inclusion types, NaCl and CaCl2, in variable proportions, dominate the solutes in the aqueous phase, whereas FeCl2 and KCl are less abundant solutes. The solutes indicate attainment of a degree of equilibrium with carbonates and schists that are interbedded with the quartzites. Some Types 1 and 2 inclusions in the inner aureole show evidence of decrepitation due to high amounts of strain and/or heating suffered by the host rocks, which suggests that they represent pore fluids that existed in the rocks prior to contact metamorphism. In addition to Type 1 inclusions, outer aureole quartzites also contain inclusions that contain CO2 vapour bubbles in addition to aqueous phase (Type 3). These inclusions only occur in interiors of granoblastic quartz that was produced by large amounts of GBM. The aqueous phase has identical ranges of first melting and final ice melting temperatures as Type 1 inclusions, suggesting that they have the same solute compositions. These inclusions are thought to represent the interstitial pore H2O that promoted recrystallization of quartz and reacted with graphite to produce CO2. Absence of significant amounts of CH4 in Type 3 inclusions is attributed to elevated fO2 that was buffered by mineral assemblages in interbedded schists. As opposed to the large amount of CO2 that was produced by the wollastonite-forming reaction in the inner aureole to inhibit GBM, the amount of CO2 produced in the outer aureole by reaction between H2O and graphite was apparently insufficient to inhibit recrystallization of quartz. [ABSTRACT FROM AUTHOR]

Tissint is an olivine-phyric shergottite from an incompatible element depleted Martian mantle source. Oxythermobarometry applied to Tissint mineral phases demonstrates that the Tissint magma underwent an increase in oxygen fugacity, from ~3.5 log units below the quarz-fayalite-magnetite ( QFM) buffer during the early stages of crystallization, to QFM−1.4 during the latter stages. This is the first time that such an oxidation event has been observed in a depleted shergottite. The reason for the oxidation event is unclear; however, calculations using the MELTS thermodynamic model suggest that auto-oxidation is insufficient to cause more than ~1 log unit of oxidation, and therefore an external oxidation mechanism-such as oxidation by degassing-is required. If volatiles are responsible for the oxidation, then it indicates that volatiles are not exclusively tied to the enriched Martian mantle reservoir. A series of experiments using the Tissint parental magma were carried out under fixed (isothermal) or variable (cooling rate) temperature control, and at either reducing ( QFM−3.2) or oxidizing ( QFM−1) redox conditions. The observed liquid line of descent supports a potential genetic relationship between basaltic shergottites and olivine-phyric shergottites. A peritectic relation where olivine is resorbed to form pyroxene is favored by increased oxygen fugacity; if oxidation during crystallization is more common than presently believed, it may explain why olivine is typically anhedral in olivine-phyric shergottites. Results from a cooling-rate experiment in which the oxygen fugacity was changed during the latter stages of crystallization resulted in olivine with a Cr compositional profile consistent with oxidized isothermal experiments, despite forming primarily under reducing conditions. A similar profile is observed in Tissint olivines, consistent with its redox history. Our results provide insights into the potential influence of oxidation events on the compositional zoning of minor or trace elements in olivine in olivine-phyric basalts. [ABSTRACT FROM AUTHOR]

The iron stable isotope compositions (δ56Fe) and iron valence states of ultrahigh-pressure eclogites from Bixiling in the Dabie orogen belt, China, were measured to trace the changes of geochemical conditions during vertical transportation of earth materials, for example, oxygen fugacity. The bulk Fe3+/ΣFe ratios of retrograde eclogites, determined by Mössbauer spectroscopy, are consistently higher than those of fresh eclogites, suggesting oxidation during retrograde metamorphism and fluid infiltration. The studied eclogites (five samples) display limited mid-ocean ridge basalts (MORB)-like (~0.10‰) δ56Fe values, which are indistinguishable from their protoliths, that is, gabbro cumulates formed through differentiation of mantle-derived basaltic magma. This suggests that Fe isotope fractionation during continental subduction is limited. Garnet separates display limited δ56Fe variation ranging from −0.08 ± 0.07 ‰ to 0.02 ± 0.07‰, whereas coexisting omphacite displays a large variation of δ56Fe values from 0.15 ± 0.07‰ to 0.47 ± 0.07‰. Omphacite also has highly variable Fe3+/ΣFe ratios from 0.367 ± 0.025 to 0.598 ± 0.024, indicating modification after peak metamorphism. Omphacite from retrograde eclogites has elevated Fe3+/ΣFe ratios (0.54-0.60) compared to that from fresh eclogites (~0.37), whereas garnet displays a narrow range of ferric iron content with Fe3+/ΣFe ratios from 0.039 ± 0.013 to 0.065 ± 0.022. The homogenous δ56Fe values and Fe3+/ΣFe ratios of garnet suggest that it survived the retrograde metamorphism and preserved its Fe-isotopic features and ferric contents of peak metamorphism. Because of similar diffusion rates of Fe and Mg in garnet and omphacite, and constant Δ26Mgomphacite-garnet values (1.14 ± 0.04‰), equilibrium iron isotope fractionation between garnet and omphacite was probably achieved during peak metamorphism. Elevated Fe3+/ΣFe ratios of omphacite from retrograde eclogites and variant Δ56Feomphacite-garnet values of the studied eclogites (0.13 ± 0.10‰ to 0.48 ± 0.10‰) indicate that oxidized geofluid infiltration resulted in the elevation of δ56Fe values of omphacite during retrograde metamorphism. [ABSTRACT FROM AUTHOR]

Multimedia models based on chemical fugacity, solved numerically, play an important role in investigating and quantifying the environmental fate of chemicals such as persistent organic pollutants. These models have been used extensively in studying the local and global distribution of chemicals in the environment. The present study describes potential sources of error that may arise from the formulation and numerical solution of environmental fugacity models. The authors derive a general fugacity equation for the rate of change of mass in an arbitrary volume (e.g., an environmental phase). Deriving this general equation makes clear several assumptions that are often not articulated but can be important for successfully applying multimedia fugacity models. It shows that the homogeneity of fugacity and fugacity capacity in a volume (the homogeneity assumption) is fundamental to formulating discretized fugacity models. It also shows that when using the fugacity rather than mass as the state-variable, correction terms may be necessary to accommodate environmental factors such as varying phase temperatures and volume. Neglecting these can lead to conservation errors. The authors illustrate the manifestation of these errors using heuristic multimedia fugacity models. The authors also show that there are easily avoided errors that can arise in mass state-variable models if variables are not updated appropriately in the numerical integration scheme. Environ Toxicol Chem 2016;35:2182-2191. © 2016 SETAC [ABSTRACT FROM AUTHOR]

Introduction: Hibonite, II(Ca,Ce,La)III,IV,V(Al,Ti,Mg,Fe,Si,V)12O19, is common in calcium-aluminum-rich inclusions (CAIs) and in the matrix of primitive chondrites. It is one of the earliest and most abundant minerals predicted to form at high temperatures (≥1500 K) from a cooling gas of solar composition [1-3]. Hibonite can incorporate several 3d transition metals (Ti being the most abundant [4-6]) on the Al cation sites (5 Wyckoff sites named hereafter M1-M5) in multiple oxidation states. The relative amounts of these cations (i.e. Ti4+/ΣTi) can potentially reflect the redox conditions under which the grain formed or last equilibrated and makes hibonite a crucial phase for understanding the thermodynamic conditions (oxygen fugacity or fO2,T, and gas composition) of the nebular gas at the time when the first solids formed [6]. However, we [6] recently outlined three main obstacles that must be resolved for hibonite to be used as an oxybarometer. For the Ti4+/ΣTi to be related to the fO2 of the nebular gas, (1) the effects of substitution reactions on the Ti oxidation state must be be characterized; (2) a comprehensive thermodynamic description (i.e. the free energy) of the phase in the pertinent thermodynamic space must be established and (3) the hibonite must have escaped secondary processing. Here we report the development of our preliminary thermodynamic description for hibonite which will aid in understanding the environment in which it formed and the local nebular thermodynamic landscape. Our goal is the development of a universal barometer applicable to any pristine hibonite grain. Samples and Methods: We determined the enthalpic (ΔH) contributions to the free energy description (ΔG) at 0K for a range of relevant hibonite solid solutions from first-principles density-functional theory (DFT) using Vienna Ab initio Simulation Package (VASP). We focused our effort on Ti, Mg, and O defects (vacancies) [4, 7] and we fixed cation substitutions to happen on M2 and M4 sites for Ti, M3 for Mg, and O4 for O vacancies within the allowed sites of the hibonite crystal chemistry [5]. To apply our thermodynamic model, we identified four hibonite grains (two in fluffy type-A CAIs and two in fine-grained spinel inclusions [8, 9]) from the reduced CV3 (3.1-3.4 [10]) chondrites Leoville (Center for Meteorite Studies, ASU collection, #821_C_3) and Efremovka (Institute of Meteoritics, UNM, #1014). Chemical mapping of the CAIs was performed using a Cameca SX-100 electron microprobe and Hitachi S-4800 scanning electron microscope (SEM) in the Kuiper Materials Imaging and Characterization Facility (KMICF) at the University of Arizona. To investigate the nanoscale composition of hibonite and to characterize its interfaces with surrounding phases, we extracted electron-transparent sections with a ThermoFisher Helios NanoLab 660 G3 focused-ion-beam scanning-electron microscope (FIB-SEM) at KMICF. The FIB sections were analyzed using a 200 keV Hitachi HF5000 aberration-corrected scanning transmission electron microscope (S/TEM) at KMICF. We measured the Ti4+/ΣTi with the electron energy-loss spectrometry method described in [6] using a Gatan Quantum ER spectrometer. Compositions was measured using an Oxford Instruments X‐Max N 100 TLE X-ray spectrometer. Results and discussion: The DFT calculations predicted ΔHmix -57.2±10 kJ/mole for CaAl12O19 (relative to standard elemental reference states). In comparison, the most favorable solid solution (at 0K) relatively to the same reference is CaAl8Ti2Mg2O19 (-92.3±10 kJ/mole). Mg2+ distribution does not impact the stability of the phase, i.e., if Mg is adjacent to or distant from the Ti4+ sites, we obtain similar values for ΔHmix, implying that, in addition to couplesubstitute with Ti4+, Mg is likely to single substitute in the structure, forming O vacancies [11]. Separately, we aimed to measure, by electron microscopy, the Ti4+/ΣTi ratio in hibonite grains with a large range of Ti/Mg ratios to test thermodynamic parameter space. However, our results show that for three of the four grains measured, the Ti/Mg=1±0.01 and Ti4+/ΣTi=1±0.03 independent of the CAI type. We note that at interfaces between hibonite and spinel, we observed Mg-rich compositions which are characteristic of chemical exchange between the grains. Nevertheless, one grain located in the core of the CAI in Leoville contains Ti/Mg>>1 and a Ti4+/ΣTi=0.81±0.03. We suggest that for most of the grain (with Ti/Mg=1) Ti or Mg was likely re-equilibrated later in the disk or in the parent-body changing the Ti4+/ΣTi. In comparison, we hypothesize that the pristine Leoville hibonite grain (Ti/Mg>>1) was not affected by secondary processes and recorded the reducing conditions of the early solar nebula forming O vacancies in the crystal structure and a low Ti4+/ΣTi. The quantification of absolute fO2 values will be discussed at the meeting. [ABSTRACT FROM AUTHOR]

Introduction: Fe-sulfides are ubiquitous in chondrites and are sensitive indicators of formation and alteration conditions in the protoplanetary disk and small Solar System bodies [e.g., 1-14]. We previously constrained a minimum oxygen fugacity (fO2) needed to form pentlandite, (Fe,Ni)9S8, [6,7] and identified trends with pentlandite compositions between distinct meteorite groups [6,7]. We also identified a relationship between the at.% Fe/S ratio of pyrrhotite group sulfides and the fO2 of formation, either in the protoplanetary disk or the parent body during aqueous alteration or thermal alteration [13]. Since pentlandite formed with pyrrhotite (they are typically intergrown in these chondrite groups [1-14]), fO2 may have influenced pentlandite compositions. To increase the information gained from individual mineral systems, here we report the chemical compositions of pentlandite in chondrites that experienced a wide range of formation and parent body alteration conditions (including fO2 [13]). This will allow us to investigate a potential trend(s) with the pyrrhotite at.% Fe/S ratio, and by extension fO2. Samples and Analytical Procedures: We determined the major and minor element compositions of pentlandite in each of the following 54 chondrites: CI (Alais), a C1-ungrouped (Miller Range [MIL] 090292), C2-ungrouped (Tarda and Tagish Lake), CY (Belgica [B]-7904), CM1/2 (Allan Hills [ALH] 83100 and Kolang [two lithologies]), unheated CM2s (Aguas Zarcas [multiple lithologies], Mighei, Queen Alexandra Range [QUE] 97990, Theil Mountains [TIL] 91722, and D'Angelo Bluff [DNG] 06004), stage I heated CM2 (Asuka [A]-881458), stage II heated CM2 (Yamato [Y]-793321), CM-like (Sutter's Mill), CO3.00 (Dominion Range [DOM] 08006), CR1 (Grosvenor Mountains [GRO] 95577), CR-an (Al Rais), CR2 (Elephant Moraine [EET] 87770, EET 92048, EET 96259, Gao-Guenie (b), Graves Nunatak [GRA] 95229, LaPaz Ice Field [LAP] 02342, LAP 04720, MIL 090657, Northwest Africa [NWA] 801, Pecora Escarpment [PCA] 91082, QUE 99177, Shişr 033, and Y-793495), shock-heated CR2 (GRO 03116), CV3OxA (Allende), CV3OxB (Bali), and CV3Red (Vigarano), CK4 (ALH 85002 and Karoonda), CK5 (Larkman Nunatak [LAR] 06868), CK6 (Lewis Cliff [LEW] 87009), L3.05 (EET 90161 and QUE 97008), LL3 (Semarkona and Vicencia), LL4 (Hamlet and Soko-Banja), LL5 (Chelyabinsk and Siena), LL6 (Appley Bridge and Saint-Séverin), R3 (MET 01149), R3.6 (LAP 031275), R5 (LAP 03639), and R6 (LAP 04840 and MIL 11207) chondrites. We acquired high-resolution backscatter electron images and quantitative chemical compositions with the JEOL-8530F Hyperprobe electron microprobe analyzer (EPMA) at Arizona State University (ASU) and the Cameca SX-100 EPMA at the Uni-versity of Arizona (UA) following [13]. Some pentlandite compositions were previously reported [6,7,10,11]. Results and Discussion: Our data show that there is a relationship between the at.% Fe/S of pyrrhotite (data from [13]) and pentlandite compositions. Since the at.% Fe/S ratio of pyrrhotite is a proxy for fO2 [13], this demonstrates that there is a relationship between fO2 and pentlandite composition. Therefore, pentlandite compositions were influ-enced by the fO2 of formation. This is true whether pentlandite formed: (1) during chondrule formation in the protoplanetary disk (i.e., during chondrule cooling, as previously noted by [6,8,10,11] for CR2, CO3.00, and LL3.00 chondrites), (2) during thermal alteration on the parent asteroid under relatively reducing (i.e., LL4-6 chondrites) or oxidizing (i.e., R4-6 and CK chondrites) conditions, or (3) during oxidizing aqueous alteration (i.e., as in CI, CM1, C1-ung, and C2-ung chondrites). Therefore, in addition to the at.% Fe/S ratio of pyrrhotite, the chemical compositions of pentlandite can also be used as a proxy for the fO2 of formation. This discovery has implications for the interpreta-tion of pentlandite compositions in meteorites and in asteroid returned samples from Ryugu and Bennu. [ABSTRACT FROM AUTHOR]

The degree to which dust enrichment enhances the oxygen fugacity ( fO2) of a system otherwise solar in composition depends on the dust composition. Equilibrium calculations were performed at 10−3 bar in systems enriched by a factor of 104 in two fundamentally different types of dust to investigate the iron oxidation state in both cases. One type of dust, called SC for solar condensate, stopped equilibrating with solar gas at too high a temperature for FeO or condensed water to be stabilized in any form, and thus has the composition expected of a nebular condensate. The other has CI chondrite composition, appropriate for a parent body that accreted from SC dust and low-temperature ice. Upon total vaporization at 2300 K, both systems have high fO2, > IW. In the SC dust-enriched system, FeO of the bulk silicate reaches ~10 wt% at 1970 K but decreases to <1 wt% below 1500 K. The FeO undergoes reduction because consumption of gaseous oxygen by silicate recondensation causes a precipitous drop in fO2. Thus, enrichment in dust having the composition of likely nebular condensates cannot yield a sufficiently oxidizing environment to account for the FeO contents of chondrules. The fO2 of the system enriched in water-rich, CI dust, however, remains high throughout condensation, as gaseous water remains uncondensed until very low temperatures. This allows silicate condensates to achieve and maintain FeO contents of 27-35 wt%. Water-rich parent bodies are thus excellent candidate sources of chondrule precursors. Impacts on such bodies may have created the combination of high dust enrichment, total pressure, and fO2 necessary for chondrule formation. [ABSTRACT FROM AUTHOR]

A novel dynamic fugacity-based model is described, developed, and tested that simulates the uptake of narcotic organic chemicals in fish from water as occurs in aquatic bioconcentration and toxicity tests. The physiologically based toxicokinetic model treats the time course of chemical distribution in 4 compartments (tissue groups) in the fish, including the liver, in which biotransformation may occur. In addition to calculating bioconcentration and toxicokinetics, 5 possible toxic endpoints are defined corresponding to chemical concentration, fugacity, or activity reaching a critical value that causes 50% mortality. The mathematical description of multicompartment uptake is simplified by expressing the equations in the fugacity format. The model is parameterized and tested against reported empirical data for the bioconcentration of pentachloroethane in rainbow trout and for uptake and mortality from aquatic exposures to naphthalene and 1,2,4-trichlorobenzene in fathead minnows. Model performance is evaluated, and it is concluded that with suitable parameterization it has potential for application for assessment of both bioconcentration and toxicity expressed as median lethal concentrations, critical body residues, and chemical activity as a function of time to death. Environ Toxicol Chem 2016;35:1257-1267. © 2015 SETAC [ABSTRACT FROM AUTHOR]