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Nominally anhydrous minerals (NAM) such as olivine are important reservoirs for water in the Earth's upper mantle, although the association of water with crystallographic defects is poorly understood. Here, hydrated regions at the atomic scale in fayalite (Fe2SiO4) are directly resolved using atom probe tomography. Site‐specific analyses reveal regions that are either compositionally homogenous or contain nanometer‐long channels that are consistent with hydrated defects. Na as a minor element is also enriched within the interlayers, indicating the formation environment is associated with Na geochemically. The ability to directly visualize and characterize hydrated regions at the nanometer scale can provide critical insight into the material properties of NAM and their impact on planetary‐scale processes, such as the influence of water‐bearing minerals on mantle rheology and geodynamics. Plain Language Summary: Anhydrous minerals such as olivine, containing seemingly small amounts of water per unit volume, are significant reservoirs of water on Earth and play a critical role in planetary geodynamics. Our knowledge of how water incorporates into these minerals is however lacking because it is challenging to actually see where the water resides in the crystal structure at the atomic scale. Here, we utilize the novel chemical imaging technique atom probe tomography to map water within minerals in three dimensions atom‐by‐atom. We find signatures for water within nanometer‐long structurally defective channels in the crystal. Sodium, thought to be a constituent of the formation environment, is also found to coincide with these defects. While the mode of water incorporation in minerals has been speculated for decades, our observations are important because it provides the first direct evidence for this occurrence. The approach developed here can be further applied to understand mechanisms for water incorporation in minerals in various environments. By understanding the fundamental properties of minerals at the atomic level, we can gain important insight into processes at the planetary scale such as the influence of water‐bearing minerals on mantle rheology. Key Points: At the planetary scale nominally anhydrous minerals are significant water reservoirs, but the mode of incorporation is poorly understoodHydrated interlayers and minor element partitioning in fayalite are visualized at the near atomic level using atom probe tomographyThis approach provides unique insight into the distribution of water in geomaterials, enabling a deeper understanding of their properties [ABSTRACT FROM AUTHOR]

This study presents new secondary ion mass spectrometry (SIMS) reference materials (RMs) for measuring water contents in nominally anhydrous orthopyroxenes from upper mantle peridotites. The enstatitic reference orthopyroxenes from spinel peridotite xenoliths have Mg#s between 0.83 and 0.86, Al2O3 ranges between 4.02 and 5.56 wt%, and Cr2O3 ranges between 0.21 and 0.69 wt%. Based on Fourier-transform infrared spectroscopy (FTIR) characterizations, the water contents of the eleven reference orthopyroxenes vary from dry to 249 ± 6 µg/g H2O. Using these reference grains, a set of orthopyroxene samples obtained from variably altered abyssal spinel peridotites from the Atlantic and Arctic Ridges as well as from the Izu-Bonin-Mariana forearc region was analyzed by SIMS and FTIR regarding their incorporation of water. The major element composition of the sample orthopyroxenes is typical of spinel peridotites from the upper mantle, characterized by Mg#s between 0.90 and 0.92, Al2O3 between 1.66 and 5.34 wt%, and Cr2O3 between 0.62 and 0.96 wt%. Water contents as measured by SIMS range from 68 ± 7 to 261 ± 11 µg/g H2O and correlate well with Al2O3 contents (r = 0.80) and Cr#s (r. = -0.89). We also describe in detail an optimized strategy, employing both SIMS and FTIR, for quantifying structural water in highly altered samples such as abyssal peridotite. This approach first analyzes individual oriented grains by polarized FTIR, which provides an overview of alteration. Subsequently, the same grain along with others of the same sample is measured using SIMS, thereby gaining information about homogeneity at the hand sample scale, which is key for understanding the geological history of these rocks. [ABSTRACT FROM AUTHOR]

Glasses are often used as models for understanding the corresponding liquid melts because they are generally assumed to share similar short and intermediate-range structural characteristics. First-principles molecular dynamics calculations have been performed to investigate the structural changes in a model basaltic (Ca22Mg14Al16Si44O148) glass at 300 K and a corresponding basaltic melt at 2500 K as a function of pressure up to 25 GPa. The results show that the local structures of the melt and glass are similar over the investigated pressure range, yet there are subtle but distinct differences. The pressure trends on the average Si–O, Ca–O, Mg–O, Al–O, O–O and Si–Si distances for the glass and melt are found to be very close. At ambient pressure, both are composed primarily of Si–O and Al-O tetrahedra. As expected, the Si–O coordination increases from four to fivefold and subsequently to sixfold. However, changes in the nearest neighbor Si–O and O–O are found to behave quite differently between the glass and melt. The most significant differences are in the distributions of the Si–O–Si and O-Si–O angles, which lead to different local structures and packing of the polyhedra. However, the differences become smaller with increased pressures indicating that caution should be exercised in the use of glasses as models for probing pressure-induced structural changes in the mantle. The calculated viscosity-pressure relationship of the basaltic melt between 0 and 25 GPa is presented and compared with available experimental data. In addition, other intrinsic properties such as the bulk modulus and sound velocity are broadly similar but not identical between the basaltic glass and melt in the broad pressure range of 0–80 GPa. [ABSTRACT FROM AUTHOR]

Earth's mantle transition zone (MTZ) is a possible global water reservoir and may be responsible for long‐term (∼100 Ma) ocean‐mass regulation. Estimates of water capacities in MTZ minerals are ∼1 wt%, far greater than that of rocks of the surrounding mantle. When water‐rich material is displaced from the MTZ, partial melting occurs, generating a sharp reduction in seismic velocities detectable with seismic receiver functions (RFs). We estimated RFs for the MTZ beneath the Yellowstone region using earthquakes recorded by ∼200 stations of the Earthscope Transportable Array. We found many LVZs both above and below the MTZ, consistent with water release upon phase transformation of hydrated MTZ rock into upper‐ and lower‐mantle mineral assemblages with low water capacities. The locations of LVZs are consistent with mid‐mantle flow induced by descent of a Farallon‐slab fragment and ascent of the deeply rooted Yellowstone plume as imaged by seismic tomography. Plain Language Summary: The Earth's mantle transition zone, located at 410–660 km depth, has been identified as a possible global water reservoir, responsible for regulating the mass of Earth's oceans over geologic time. Water is transported in hydrated minerals to the transition zone by the subduction of plates and it is returned to the oceans by plumes. Transition zone rock has a water‐storage capacity of ∼1.0 wt%. Upper‐ and lower‐mantle rock has a much lower capacity for water, on the order of 0.1 wt%. Due to the significant discrepancy in water‐storage capacity, when hydrated minerals leave the transition zone, the rock partially melts. Sharp boundaries associated with partial‐melt layers can reduce the velocities of seismic waves by a few percent, which is detectable using seismic waves that convert at the interface between rock with and without partial melt. The Yellowstone region provides an opportunity to seek hydrous partial melting above and below the transition zone because both a subducting slab and an upwelling plume are thought to be present. The pattern of low‐velocity layers detected underneath Yellowstone is consistent with the expected rock flow for a plume that originates within the lower mantle. Key Points: Seismic low‐velocity zones (LVZs) are observed above and below the mantle transition zone (MTZ) surrounding the Yellowstone hotspotThe Yellowstone plume and Farallon slab may displace hydrous MTZ rock to release water via mineral phase change to cause the LVZsThe weak LVZ directly above the Yellowstone plume suggests that ascending rock is relatively dry, consistent with a lower‐mantle upwelling [ABSTRACT FROM AUTHOR]

Background: The prevalent rate of incontinence-associated dermatitis (IAD) trends upward in older populations. Skin breakdown from IAD impacts the quality of life of older adults and reflects the quality of care in hospitals and long-term care facilities. Specific and appropriate interventions for prevention and care are needed. This systematic review aims to review optimal strategies for prevention and care for older adults with IAD. Methods: PubMed, CINAHL, SCOPUS, Medline, ProQuest, ThaiLIS, ThaiJo, and E-Thesis were searched for articles published between January 2010 and December 2020. Only articles focusing on older adults were included for the review. Results: Eleven articles met the inclusion/exclusion criteria. Interventions for the prevention and care of IAD among older adults were categorized as assessment, incontinence management/causative factors management, cleansing, application of medical products for both skin moisturizing and skin barrier, body positioning, nutrition promotion, health education and training, and outcome evaluation. Specific prevention and care strategies for older adults with IAD included using specific assessment tools, applying skin cleansing pH from 4.0 to 6.8, body positioning, and promoting food with high protein. Other strategies were similar to those reported for adult patients. Conclusion: The systematic review extracted current and specific prevention and care strategies for IAD in older adults. The prevention and care strategies from this systematic review should be applied in clinical practice. However, more rigorous research methodology is recommended in future studies, especially in examining intervention outcomes. Nurses and other health professionals should be educated and trained to understand the causes of IAD in older adults and the specific prevention and care strategies for this population. Because older adults are prone to skin damage, and this type of skin breakdown differs from pressure ulcers, the tools for assessment and evaluation, and the strategies for prevention and care require special attention. Prospero Registration Number: CRD42021251711. [ABSTRACT FROM AUTHOR]

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Glassy melt inclusions are unique geological repositories that preserve evidence of the formation and evolution of mantle and crustal-derived magmas. However, the mechanisms responsible for their preservation in slowly cooled crustal rocks remain contentious, in some part due to their small size (commonly < 10 µm) and the technical difficulty in quantifying composition and microstructures. In this work, time-of-flight secondary ion mass spectrometry, transmission electron microscopy and atom probe tomography are used to characterize glassy melt inclusions found in peritectic garnets of a migmatite from the Spanish Betic Cordillera. The glassy melt inclusions coexist in a close spatial relationship with partially to totally crystallized melt inclusions (nanogranitoids). Analyses of the glassy inclusions show a heterogeneous, patchy distribution of Na and K within the glass and along inclusion walls. Nanoscale spherical domains of Al, Fe, K, Na, Cl and Li are also found systematically distributed at inclusion edges, and are interpreted to represent pre-nucleation clusters. The location and compositional similarity of these clusters with micas and feldspars in nanogranitoids indicate that the glassy inclusions represent former nanogranitoids "captured" at an earlier stage of crystallization, suggesting a likely common origin for both the glassy inclusions and nanogranitoids. A comparison between the composition of melt inclusions with previously published data reveals that preserved glassy inclusions contain significant less H2O (av. 2.72 wt%) than nanogranitoids (average of 6.91 wt%). This suggests the low-H2O content representing a further impediment to crystallization, along with the very small volume of these cavities, favouring the coexistence of glassy inclusions and nanogranitoids. In contrast, crystal nucleation is enhanced in more hydrous melts, where H2O reduces melt viscosity and promotes diffusion. [ABSTRACT FROM AUTHOR]

Inclusions of relic high-pressure melts provide crucial information on the fate of crustal rocks in the deep roots of orogens during collision and crustal thickening, including at extreme temperature conditions exceeding 1000 °C. However, discoveries of high-pressure melt inclusions are still a relative rarity among case studies of inclusions in metamorphic minerals. Here we present the results of experimental and microchemical investigations of nanogranitoids in garnets from the felsic granulites of the Central Maine Terrane (Connecticut, U.S.A.). Their successful experimental re-homogenization at ~2 GPa confirms that they originally were trapped portions of deep melts and makes them the first direct evidence of high pressure during peak metamorphism and melting for these felsic granulites. The trapped melt has a hydrous, granitic, and peraluminous character typical of crustal melts from metapelites. This melt is higher in mafic components (FeO and MgO) than most of the nanogranitoids investigated previously, likely the result of the extreme melting temperatures—well above 1000 °C. This is the first natural evidence of the positive correlation between temperature and mafic character of the melt; a trend previously supported only by experimental evidence. Moreover, it poses a severe caveat against the common assumption that partial melts from metasediments at depth are always leucogranitic in composition. NanoSIMS measurement on re-homogenized inclusions show significant amounts of CO2, Cl, and F. Halogen abundance in the melt is considered to be a proxy for the presence of brines (strongly saline fluids) at depth. Brines are known to shift the melting temperatures of the system toward higher values and may have been responsible for delaying melt production via biotite dehydration melting until these rocks reached extreme temperatures of more than 1000 °C, rather than 800-850 °C as commonly observed for these reactions. [ABSTRACT FROM AUTHOR]

Featured Application: The investigations provide information about important parameters needed for the modelling of design bases, and beyond design bases, nuclear accidents and processes occurring during the long-term dry storage of spent nuclear fuel. In situ neutron radiography experiments can provide information about diffusive processes and the kinetics of chemical reactions. The paper discusses requirements for such investigations. As examples of the zirconium alloy Zircaloy-4, the hydrogen diffusion, the hydrogen uptake during high-temperature oxidation in steam, and the reaction in nitrogen/steam and air/steam atmospheres, results of in situ neutron radiography investigations are reviewed, and their benefit is discussed. [ABSTRACT FROM AUTHOR]

Hydrous Fo91 ringwoodite crystals were synthesized at 20 GPa and high-temperature conditions using a multi-anvil press. Recovered crystals were analyzed using electron microprobe analysis, Raman spectroscopy, infrared spectroscopy, synchrotron Mössbauer spectroscopy, single-crystal X-ray diffraction, and single-crystal Laue neutron diffraction, to carefully characterize the chemistry and crystallography of the samples. Analysis of the combined data sets provides evidence for the presence of tetrahedrally coordinated ferric iron and multiple hydrogen incorporation mechanisms within these blue-colored iron-bearing ringwoodite crystals. Tetrahedral ferric iron is coupled with cation disorder of silicon onto the octahedrally coordinated site. Cation disorder in mantle ringwoodite minerals may be promoted in the presence of water, which could have implications for current models of seismic velocities within the transition zone. Additionally, the presence of tetrahedrally coordinated ferric iron may cause the blue color of many ringwoodite and other high-pressure crystals. [ABSTRACT FROM AUTHOR]

Wadsleyite can store significant amounts of H2O in its crystal structure as hydroxyl. However, H2O solubility in Fe‐bearing wadsleyite remains poorly constrained at mantle transition zone temperatures. Previous studies (e.g., Demouchy et al., 2005 [https://doi.org/10.2138/am.2005.1751]; Litasov et al., 2011 [https://doi.org/10.1007/s00269-010-0382-3]) focused primarily on Fe‐free systems, which do not represent the Earth's interior because Fe may affect the H2O solubility. Here, we investigated the temperature dependence of H2O solubility in Fe‐bearing and Fe‐free wadsleyite at 1500–2100 K. The results indicate that H2O solubility in Fe‐bearing wadsleyite is higher than in Fe‐free samples at 1800–1900 K, corresponding to transition zone geotherm, but there is no clear Fe content dependence in the Fe‐bearing samples. Wadsleyite can contain approximately 1.0 wt.% H2O at transition zone temperatures. The H2O solubility in wadsleyite is lower than ringwoodite along a plume geotherm, which may result in dehydration melting at the 520‐km discontinuity by upwelling flow in plumes. Plain Language Summary: The mantle transition zone at 410–660 km depth is a H2O sponge because wadsleyite and ringwoodite can contain large amounts of H2O in their crystal structures as hydroxyl defects. However, the solubility of H2O in Fe‐bearing wadsleyite is poorly constrained compared with ringwoodite and Fe‐free wadsleyite, which have been extensively investigated. The exact H2O storage capacity of the mantle transition zone, therefore, remains unknown. Here, we investigated the solubility of H2O in Fe‐bearing wadsleyite as a function of temperature. The results indicate that wadsleyite can store ∼1.0 wt.% H2O at transition zone temperatures and ∼0.65 wt.% along a plume geotherm. H2O solubility in wadsleyite is lower than that in ringwoodite in mantle plumes. A dehydration melting layer at the 520‐km discontinuity near plumes can, therefore, form via the phase transition from ringwoodite to wadsleyite under H2O‐saturated conditions driven by upwelling flow in mantle plumes. Key Points: H2O solubility in Fe‐bearing wadsleyite decreases with increasing temperatureFe‐bearing wadsleyite can contain ∼1.0 wt.% H2O at mantle transition zone temperatureDehydration melting could occur at the 520‐km discontinuity by upwelling flow near plumes [ABSTRACT FROM AUTHOR]

Volatile elements (water, carbon, nitrogen, sulfur, halogens, and noble gases) played an essential role in the secular evolution of the solid Earth and emergence of life. Here we provide an overview of Earth's volatile inventories and describe the mechanisms by which volatiles are conveyed between Earth's surface and mantle reservoirs, via subduction and volcanism. Using literature data, we compute volatile concentration and flux estimates for Earth's major volatile reservoirs and provide an internally balanced assessment of modern global volatile recycling. Using a nitrogen isotope box model, we show that recycling of N (and possibly C and S) likely began before 2 Ga and that ingassing fluxes have remained roughly constant since this time. In contrast, our model indicates recycling of H2O(and most likely noble gases) was less efficient in the past. This suggests a decoupling of major volatile species during subduction through time, which we attribute to the evolving thermal regime of subduction zones and the different stabilities of the carrier phases hosting each volatile. This review provides an overview of Earth's volatile inventory and the mechanisms by which volatiles are transferred between Earth reservoirs via subduction. The review frames the current thinking regarding how Earth acquired its original volatile inventory and subsequently evolved through subduction processes and volcanism. [ABSTRACT FROM AUTHOR]

We investigate the coupling between H, minor, trace, and ultra-trace element incorporations in 17 olivines from ten different locations covering various petrological origins: magmatic, hydrothermal, and mantle-derived context. Concentrations in major element are determined by micro X-ray fluorescence. Minor, trace, and ultra-trace elements are determined by laser ablation inductively coupled plasma mass spectrometry. Hydrogen concentrations are quantified using unpolarized and polarized Fourier transform infrared spectroscopy (FTIR). Forsterite contents (83.2–94.1%) reflect the petrogenetic diversity. Hydrogen concentrations range from 0 to 54 ppm H2O wt. Minor element concentrations (Ni + Mn) range from 3072 to 4333 ppm, and impurities are dominated by Ni, Mn, Ca or B. Total trace element concentrations range from 8.2 to 1473 ppm. Total rare Earth and extended ultra-trace elements concentrations are very low (< 0.5 ppm). Magmatic and hydrothermal olivines show the most and least amount of impurities, respectively, and mantle-derived olivines have concentrations between these two extremes. Combined with minor, trace, and ultra-trace element concentrations, the hydrogen concentrations, and FTIR OH bands reflect the point defect diversity imposed by different geological settings. Hydrogen concentrations are inversely correlated with divalent impurities, indicating their competition for vacancies. However, a broad positive correlation is also found between OH bands at 3575 and 3525 cm−1 and Ti, confirming the existence of Ti-clinohumite-like point defect in mantle olivines. Nonetheless, Ti does not exclusively control hydrogen incorporation in olivine due to the co-existence with other mechanisms, and its effect appears diluted. Our results confirm that hydrogen behaves as a peculiar incompatible element, and furthermore as an opportunistic impurity in olivine. [ABSTRACT FROM AUTHOR]

The study of nominally anhydrous minerals with vibrational spectroscopy, despite its sensitivity, tends to produce large uncertainties (in absorbance or intensity) if the observed dispersion of the values arising from the anisotropy of interaction with light in non-cubic minerals is not assessed. In this study, we focused on Raman spectroscopy, which allows the measurement of crystals down to a few micrometers in size in backscattered geometry, and with any water content, down to 200 ppm by weight of water. Using synthetic hydrous single-crystals of olivine and wadsleyite, we demonstrate that under ideal conditions of measurement and sampling, the data dispersion reaches ±30% of the average (at 1σ) for olivine and ±32% for wadsleyite, mostly because of their natural anisotropy. As this anisotropy is linked to physical properties of the mineral, it should not be completely considered as an error without treatment. By simulating a large number of measurements with a 3D model of the OH/Si spectral intensity ratio for olivine and wadsleyite as a function of orientation, we observe that although dispersion increases when increasing the number of measured points in the sample, analytical error decreases, and the contribution of anisotropy to this error decreases. With a sufficient number of points (five to ten, depending on the measurement method), the greatest contribution to the error on the measured intensities is related to the instrument's biases and reaches 12 to 15% in ideal cases, indicating that laser and power drift corrections have to be carefully performed. We finally applied this knowledge on error sources (to translate data dispersion into analytical error) on olivine and wadsleyite standards with known water contents to build calibration lines for each mineral to convert the intensity ratio of the water bands over the structural bands (OH/Si) to water content. The conversion factors from OH/Si to parts per million by weight of water (H2O) are 93 108 ± 24 005 for olivine, 250 868 ± 53 827 for iron-bearing wadsleyite, and 57 862 ± 12 487 for iron-free wadsleyite, showing the strong effect of iron on the spectral intensities. [ABSTRACT FROM AUTHOR]

Partial melting up to ultra high temperature (UHT) conditions is one of the major processes for the geochemical differentiation and reworking of the mid‐ to lower continental crust, with relevant implications on its rheological behaviour. UHT granulites from the Gruf Complex (European Central Alps) display garnet and sapphirine porphyroblasts containing a variety of primary melt inclusions (MI). Typically, MI in garnet occur as glassy and polycrystalline inclusions (i.e. nanogranitoids), the latter commonly organized in mm‐sized clusters associated with primary fluid inclusions (FI). Nanogranitoids are characterized by an elliptical faceted shape, with variable sizes ranging from 2 to 115 µm, while glassy inclusions show negative crystal shapes that usually never exceed 15 µm in diameter and present CO2‐rich shrinkage bubbles. The characteristic mineral assemblage observed in nanogranitoids consists of quartz, biotite, muscovite, plagioclase, K‐feldspar, kokchetavite and rarely aluminosilicates. Glassy and re‐homogenized MI are peraluminous and rhyolitic in composition, with SiO2 = 69 − 80 wt% and Na2O + K2O = 5 − 12 wt%. Commonly, the analysed MI have very high K2O (>6 wt%) and very low Na2O (<2 wt%) contents, indicative for potassic to ultrapotassic melts. Measured H2O contents of the melts range from 2.9 to 8.8 wt%, whereas CO2 concentrations are between 160 and 1738 ppm. Accordingly, calculated viscosities for re‐homogenized MI vary between 104 and 105 Pa·s. Related primary FI mainly contain CO2, with rare occurrence of CO and N2, and are commonly associated with quartz, as well as different carbonates and phyllosilicates. It is assumed that the source for the carbonic fluid was external and probably related to the degassing lithospheric mantle. Consequently, it is argued that anatexis was initially triggered by incongruent dehydration melting reactions involving biotite breakdown and proceeded in the presence of an externally derived COH‐bearing fluid. The coexistence of COH‐bearing fluid and MI indicates that partial melting occurred under conditions of fluid − melt immiscibility. Potassic to ultrapotassic MI in UHT granulites suggests that lower crustal anatexis may play a significant role in the redistribution of heat‐producing elements (such as K2O), potentially influencing the thermal structure of the continental crust. [ABSTRACT FROM AUTHOR]

Amphiboles are hydrous minerals that are formed in the oceanic crust via hydrothermal alteration. The partial substitution of halogens for OH− makes amphibole one of the principal hosts of Cl and F in the subducting slab. In this study, we investigated the electrical conductivity of a suite of halogen bearing amphibole minerals at 1.5 GPa up to 1,400 K. The discontinuous electrical behavior indicates dehydration of amphibole at ∼915 K. This is followed by dehydration induced hydrous melting at temperatures above 1,070 K. We find that the released aqueous fluids have an electrical conductivity of ∼0.1 S/m. This high electrical conductivity is likely to explain anomalously high electrical conductivity observed in certain subduction zone settings. This high electrical conductivity of an order of magnitude greater than the electrical conductivity of pure aqueous fluids at similar conditions is likely due to the partitioning of the F and Cl into the aqueous fluids. We also noted that subsequent to the dehydration, secondary phases form due to the breakdown of the primary halogen bearing amphibole. Chemical analyses of these secondary phases indicate that they are repositories of F and Cl. Hence, we infer that upon dehydration of the primary halogen bearing amphibole, first the F and Cl are partitioned into the aqueous fluids and then the halogens are partitioned back to the secondary mineral phases. These secondary minerals are likely to transport the halogen to the deep Earth and may in part explain the halogen concentration observed in ocean island basalt. Plain Language Summary: Amphiboles are one of the principal mineral phases that accommodate halogens in the subducting slab. The aqueous fluid released during the dehydration of amphibole dissolves and transfers halogens into the overlying wedge mantle. The resulting fluid exhibits high electrical conductivity. Our study also indicates that a significant portion of F and small quantities of Cl carried by amphibole are partitioned back to the secondary mineral phases that result from the breakdown of the primary amphibole. These secondary mineral phases are likely to transport halogen into the Earth's interior and may explain the distinct halogen contents observed between lower mantle‐derived ocean island basalts compared to MORB sources. Key Points: The presence of F and Cl increases the electrical conductivity in aqueous fluidsDuring dehydration, a fraction of F and Cl partitions into solid phasesF and Cl can be transported to the deep mantle by secondary minerals [ABSTRACT FROM AUTHOR]

Understanding the transformations of highly reduced enstatite chondrites (EC) in terrestrial environments, even on very short timescales, is important to make the best use of the cosmochemical and mineralogical information carried by these extraterrestrial rocks. Analogs of EC meteorites were synthesized at high pressure and high temperature. Then, their aqueous alterations, either abiotic or in the presence of the bacteria Acidithiobacillus ferrooxidans or Acidithiobacillus thiooxidans, were studied under air, at pH ~2, 20 °C, and atmospheric pressure. They stayed in shaken batch reactors for 15 days. Reference experiments were carried out separately by altering only one mineral phase among those composing the synthetic EC (i.e., sulfides: troilite or Mg‐Ca‐rich sulfides, enstatite, and Fe70Si30). Composition of the alteration aqueous media and microstructures of the weathered solids were monitored by inductively coupled plasma atomic emission spectroscopy and by scanning electron microscopy, respectively. Alteration sequence of the different mineral components of the synthetic EC was found to occur in the following order: magnesium‐calcium sulfides > troilite > iron‐silicon metallic phase > enstatite regardless of the presence or absence of the microorganisms. Such small biological effects might be due to the fact that the alteration conditions are far from biologically optimal, which is likely the case in most natural environments. The exposed surfaces of an EC meteorite falling on Earth in a wet and acidic environment could lose within a few hours their Ca‐ and Mg‐rich sulfides (oldhamite and niningerite). Then, in <1 week, troilite and kamacite could be altered. In a wet and acidic environment, only the enstatite would remain intact and would weather on a much slower geological timescale. [ABSTRACT FROM AUTHOR]

The glass transition temperature (Tg) is a key parameter to investigate for application in nuclear waste immobilization in borosilicate glasses. Tg for several glasses containing iodine (I) has been measured in order to determine the I effect on Tg. Two series of glass composition (ISG and NH) containing up to 2.5 mol% I and synthesized under high pressure (0.5 to 1.5 GPa) have been investigated using differential scanning calorimetry (DSC). The I local environment in glasses has been determined using X‐ray photoelectron spectroscopy and revealed that I is dissolved under its iodide form (I−). Results show that Tg is decreased with the I addition in the glass in agreement with previous results. We also observed that this Tg decrease is a strong function of glass composition. For NH, 2.5 mol% I induces a decrease of 24°C in Tg, whereas for ISG, 1.2 mol% decreases the Tg by 64°C. We interpret this difference as the result of the I dissolution mechanism and its effect on the polymerization of the boron network. The I dissolution in ISG is accompanied by a depolymerization of the boron network, whereas it is the opposite in NH. Although ISG corresponds to a standardized glass, for the particular case of I immobilization it appears less adequate than NH considering that the decrease in Tg for NH is small in comparison to ISG. [ABSTRACT FROM AUTHOR]

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]

Water has a strong effect on silicate melt properties, yet its dissolution mechanism in depolymerized melts, typical for mantle composition, remains poorly understood. Here we report results of first‐principles molecular dynamics simulations for hydrous Mg2SiO4 melts with 6, 16, and 27 wt% H2O at pressure and temperature conditions relevant to the upper mantle and mantle transition zone. The results show that hydrogen bonds not only to the network‐forming cation Si but also to Mg which—nevertheless—remains the most important network modifier. There is no evidence to support the hypothesis based on experimental data that water may cause an increase in melt polymerization for ultramafic magmas; the ratio of non‐bridging oxygen per Si increases with the addition of the oxygen from H2O. The partial molar volume of water is independent on concentration in our simulations which allows us to examine the density of hydrous melt systematically. The critical water content—at which melts are neutrally buoyant compared to the surrounding mantle—is ~4 wt% H2O for a pyrolite composition, much lower than the high water content (>10 wt%) observed in petrological experiments and estimated thermodynamically for low‐degree partial melts formed in the vicinity of the mantle transition zone. Plain Language Summary: Geophysical observations indicate abrupt changes in the material properties of the Earth's mantle right below and above the transition zone, at a depth between 410 and 660 km. The existence of low‐velocity and high conductivity layers near this region is often taken as an indication for melting caused by the presence of water. However, the density of such hydrous melts is not well characterized over the relevant pressure‐temperature range. Here we present new simulations on Mg2SiO4 melts with a wide range of water concentrations to address this issue. The water content at which hydrous melts have the same density as the surrounding mantle is about 4 wt%, much lower than the high water content (>10 wt%) estimated for melts occurring in the Earth's mantle, suggesting they cannot experience long‐term gravitational stability in the mantle transition zone and its vicinity. We further find that water does not cause a significant change in melt structure as proposed previously. Key Points: We perform ab initio molecular dynamics simulations on Mg2SiO4 melts over a wide range of H2O concentrationsWe find no evidence for an increase in the degree of melt polymerization with water for ultramafic magmas as proposed previouslyThe critical water content at which hydrous peridotitic melts have the same density as the surrounding mantle is about 4 wt% [ABSTRACT FROM AUTHOR]

Interpretation of electrical conductivity anomalies observed in magnetotelluric models provides an important opportunity to understand the nature of the lithospheric mantle and its dynamics. Over the course of the last two decades, a great number of experimental petrology studies have been carried out which can be utilized to construct electrical conductivity distribution models for a given composition and geotherm. We have developed an open-source software (MATE, Mantle Analysis Tool for Electromagnetics) with an easy-to-use graphical interface that creates such theoretical models. The program is developed in such a way that additional effects and models can be added very easily. To investigate the conductivity distribution of the cratonic mantle, a series of experiments was made. Results indicate that it is of utmost importance to analyze the magnetotelluric models using accurate compositions, water distributions, and geometric models. Hence, using only olivine conductivity models can lead to erroneous interpretations of both conductivity and estimated water content. Analysis of the potential causes for conductive anomalies shows that the upper and lower lithospheric mantle can be interpreted separately with the transition between them at 75-125 km. Conductive anomalies in the upper lithospheric mantle (<1,000 Ωm) are likely to be explained by the existence of well-connected minor phases associated with metasomatic fluids, whereas in the lower lithospheric mantle, hydration and/or well-connected minor phases (e.g., phlogopite or amphibole) can explain conductive anomalies. [ABSTRACT FROM AUTHOR]

Hydrogen concentrations in minerals of peridotite xenoliths in alkali basaltic rocks from Quaternary volcanoes in northwest Spitsbergen were measured using polarized Fourier transform infrared spectroscopy (FTIR) to trace the effects of geologic processes on hydrogen distribution in the continental lithospheric mantle. The mineral grains show hydrogen profiles with lower concentrations at rims suggesting diffusive hydrogen loss during the entrapment and transport of the xenoliths in magma. However, hydrogen concentrations in the centers of the grains are uniform and appear to represent hydrogen abundances in the Spitsbergen upper mantle. The olivine, orthopyroxene, and clinopyroxene contain 1–10, 130–290, and 350–560 ppm H2O, respectively. Hydrogen abundances away from metasomatic melt conduits recorded by Type 1 xenoliths are correlated with the concentrations of incompatible trace elements, indicating that hydrogen distribution is related to mantle metasomatism. By contrast, hydrogen near the melt conduits, recorded by Type 2 xenoliths, shows no regular correlations with incompatible trace elements (except Nb in clinopyroxene) and may be affected by fractional crystallization of amphibole in the conduits. Hydrogen contents decrease away from the melt conduits and are controlled by the interaction between the depleted host mantle and percolating metasomatic melts. Therefore, the metasomatic melt could have variably hydrated the Spitsbergen upper mantle via different processes. The H2O/Ce ratios of the melt in equilibrium with clinopyroxene near the metasomatic melt conduits range from 93 to 218, i.e., within the oceanic island basalt (OIB) range. This is consistent with that the metasomatic melt could have been derived from OIB-type sources evidenced by the Sr-Nd isotope compositions of the xenoliths. [ABSTRACT FROM AUTHOR]

We explore the partitioning behavior of hydrogen between coexisting metal and silicate melts at conditions of the magma ocean and the current core–mantle boundary with the help of density functional theory molecular dynamics. We perform simulations with the two‐phase and thermodynamic integration methods. We find that hydrogen is weakly siderophile at low pressure (20 GPa and 2,500 K), and becomes much more strongly so with pressure, suggesting that hydrogen is transported to the core in a significant amount during core segregation and is stable there. Based on our results, the core likely contains ~1 wt% H, assuming single‐stage formation and equilibration at 40 GPa. Our two‐phase simulations further suggest that silicon is entrained in the core‐forming metal, while magnesium remains in the silicate phase. This preferred incorporation of silicon hints at an explanation for the elevated Mg/Si ratio of the bulk silicate Earth relative to chondritic compositions. Plain Language Summary: Hydrogen is the most abundant element in the universe and may be present in the Earth's core together with its main constituent, iron. Despite its importance, the amount of hydrogen in the core has been poorly understood as it is extremely difficult to measure the hydrogen content in iron metal from experiments at high pressure and temperature. Here, we use advanced quantum mechanical simulations on silicate and metallic melts showing that hydrogen becomes increasingly more incorporated in metal over silicate at high pressure and temperature, conditions under which Earth's core formed. Therefore, hydrogen can be present in the core in high abundance. We further show that silicon is also transported to the core to a smaller extent, while magnesium remains in the mantle material. Key Points: We perform density functional theory molecular dynamics simulations to study hydrogen partitioning between liquid metal and silicateHydrogen is predicted to be weakly siderophile at low pressure (~20 GPa) and becomes significantly more siderophile at higher pressuresCore segregating from the magma ocean may have sequestered significant amounts of H and, to a lesser extent, Si, but little or no Mg [ABSTRACT FROM AUTHOR]

In Part 1 of this study (Yabe et al., 2020, https://doi.org/10.1029/2020JB019415), we established an olivine grain‐boundary diffusion creep law that incorporates the chemically induced enhancement of creep rates, which becomes significant with increasing temperature. The effect was attributed to grain‐boundary disordering that starts at ~0.92 × solidus (bulk eutectic temperature). In this study, we estimated solidus temperatures of the samples used in the previous diffusion creep experiments. These temperatures were used to compare previously reported diffusion creep rates for olivine with our established diffusion creep law. We found that the law explains a difference of up to 2 orders of magnitude in olivine creep rates at the same temperatures, stresses, grain sizes, and water contents in the previous studies. The geotherm normalized by the mantle solidus was calculated for the upper mantle with water contents ranging from 0 to 300 μg/g, which predicts depths where grain‐boundary diffusion creep is enhanced due to grain‐boundary disordering. Constructed viscosity‐depth profiles reveal a very thin mantle lithosphere beneath mid‐ocean ridges, with development of the lithosphere away from the ridge, leaving a low‐viscosity region below. Given a grain size of 1 mm and depending on the water content, a viscosity of 2–5 × 1019 Pa·s is predicted for the low‐viscosity mantle beneath 50‐million‐year‐old seafloor. Key Points: Solidus‐dependent grain‐boundary diffusion creep explains differences among previous olivine diffusion creep resultsEnhanced grain‐boundary diffusion creep at >0.92 × solidus results in weakening of the upper mantleDepth profiles of viscosity based on grain‐boundary diffusion creep in the oceanic upper mantle are presented [ABSTRACT FROM AUTHOR]

Understanding the behavior of halogens (Cl, Br, and I) in subduction zones is critical to constrain the geochemical cycle of these volatiles and associated trace metals, as well as to quantify the halogen fluxes to the atmosphere via volcanic degassing. Here, the partitioning of bromine between coexisting aqueous fluids and hydrous granitic melts and its speciation in slab-derived fluids have been investigated in situ up to 840 ∘ C and 2.2 GPa by synchrotron x-ray fluorescence (SXRF) and x-ray absorption spectroscopy (XAS) in diamond anvil cells. The partition coefficients DBrf/m range from ∼2 to ∼15 , with an average value of 6.7±3.6 (1σ) over the whole pressure–temperature (P – T) range, indicating a moderate Br enrichment in aqueous fluids, in agreement with previous work. Extended x-ray-absorption fine-structure (EXAFS) analysis further evidences a gradual evolution of Br speciation from hydrated Br ions [Br(H2O) 6 ] - in slab dehydration fluids to more complex structures involving both Na ions and water molecules, [ BrNax(H2O)y ], in hydrous silicate melts and supercritical fluids released at greater depth (> 200 km). In denser fluids (ρ > 1.5 g cm -3) containing 60 wt % dissolved alkali–silicates and in hydrous Na2Si2O5 melts (10 wt % H2O), Br is found to be in a "salt-like" structure involving the six nearest Na ions and several next-nearest O neighbors that are either from water molecules and/or the silicate network. Bromine (and likely chlorine and iodine) complexing with alkalis is thus an efficient mechanism for the mobilization and transport of halogens by hydrous silicate melts and silica-rich supercritical fluids. Our results suggest that both shallow dehydration fluids and deeper silicate-bearing fluids efficiently remove halogens from the slab in the sub-arc region, thus favoring an efficient transfer of halogens across subduction zones. [ABSTRACT FROM AUTHOR]

The presence of nanogranitoids (crystallized melt inclusions showing a granitic s.l. composition) in regionally metamorphosed migmatitic and granulitic terranes was documented for the first time in 2009. This important finding represented a hallmark event for crustal petrologists, demonstrating that the pristine composition of anatectic melts may be preserved and recovered in small objects hosted in peritectic minerals of high-grade metamorphic rocks. Many further occurrences were documented in rocks worldwide, from diverse geodynamic settings, from the Archean to Miocene, and these inclusions turned out to have diverse composition (from silicatic to carbonatitic). Therefore, we propose "nanorocks" as a comprehensive name for these crystallized melt inclusions. In the last decade, many studies demonstrated their utility in characterizing mechanisms of melting and in tracking crustal magma evolution. Although scholars are now able to easily recognize nanorocks in high-grade metamorphic rocks, only a few research groups remelt them by means of experimental devices because of a time-consuming preparation. However, when cutting-edge techniques are applied in addition to more routine ones, nanorocks do open new perspectives in crustal petrology. [ABSTRACT FROM AUTHOR]

The volcanic degassing of halogens, and especially of the heavier Br and I, received increased attention over the last 20 years due to their significant effect on atmospheric chemistry, notably the depletion of stratospheric ozone. While the effect of melt composition on halogen diffusion, solubility, or fluid-melt partitioning in crustal magma chambers has been thoroughly studied, structural controls on halogen incorporation in silicate melts remain poorly known, with only few studies available in simplified borosilicate or haplogranite compositions. Here, we demonstrate that high-energy resolution fluorescence detection X -ray absorption spectroscopy (HERFD-XAS) with a crystal analyzer spectrometer (CAS) is well-suited for the study of Br speciation in natural volcanic glasses which can contain lower Br concentrations than their laboratory analogs. Especially, HERFD-XAS results in sharper and better-resolved XANES and EXAFS features than previously reported and enables detection limits for EXAFS analysis down to 100 ppm when previous studies required Br concentrations above the 1000 ppm level. XANES and EXAFS analyses suggest important structural differences between synthetic haplogranitic glass, where Br is surrounded by Na and next-nearest oxygen neighbors, and natural volcanic glasses of basaltic to rhyodacitic compositions, where Br is incorporated in at least three distinct sites, surrounded by Na, K, or Ca. Similar environments, involving both alkali and alkaline earth metals have already been reported for Cl in Ca-bearing aluminosilicate glass and our study thus underlines that the association of Br with divalent cations (Ca2+) has been underestimated in the past due to the use of simplified laboratory analogs. Overall, similarities in Cl and Br structural environments over a large array of compositions (46-67 wt% SiO2) suggest that melt composition alone may not have a significant effect on halogen degassing and further support the coupled degassing of Cl and Br in volcanic systems. [ABSTRACT FROM AUTHOR]

Water and iron are believed to be key constituents controlling the strength and density of the lithosphere and, therefore, play a crucial role in the long-term stability of cratons. On the other hand, metasomatism can modify the water and iron abundances in the mantle and possibly triggers thermomechanical erosion of cratonic keels. Whether local or large scale processes control water distribution in cratonic mantle remains unclear, calling for further investigation. Spinel peridotite xenoliths in alkali basalts of the Cenozoic Tok volcanic field sampled the lithospheric mantle beneath the southeastern margin of the Siberian Craton. The absence of garnet-bearing peridotite among the xenoliths, together with voluminous eruptions of basaltic magma, suggests that the craton margin, in contrast to the central part, lost its deep keel. The Tok peridotites experienced extensive and complex metasomatic reworking by evolved, Ca-Fe-rich liquids that transformed refractory harzburgite to lherzolite and wehrlite. We used polarized Fourier transform infrared spectroscopy (FTIR) to obtain water content in olivine, orthopyroxene (Opx), and clinopyroxene (Cpx) of 14 Tok xenoliths. Olivine, with a water content of 0-3 ppm H2O, was severely degassed, probably during emplacement and cooling of the host lava flow. Orthopyroxene (49-106 ppm H2O) and clinopyroxene (97-300 ppm H2O) are in equilibrium. The cores of the pyroxene grains, unlike olivine, experienced no water loss due to dehydration or addition attributable to interaction with the host magma. The water contents of Opx and Cpx are similar to those from the Kaapvaal, Tanzania, and North China cratons, but the Tok Opx has less water than previously studied Opx from the central Siberian craton (Udachnaya, 28-301 ppm; average 138 ppm). Melting models suggest that the water contents of Tok peridotites are higher than in melting residues, and argue for a post-melting (metasomatic) origin. Moreover, the water contents in Opx and Cpx of Tok peridotites are decoupled from iron enrichments or other indicators of melt metasomatism (e.g., CaO and P2O5). Such decoupling is not seen in the Udachnaya and Kaapvaal peridotites but is similar to observations on Tanzanian peridotites. Our data suggest that iron enrichments in the southeastern Siberian craton mantle preceded water enrichment. Pervasive and large-scale, iron enrichment in the lithospheric mantle may strongly increase its density and initiate a thermo-magmatic erosion. By contrast, the distribution of water in xenoliths is relatively "recent" and was controlled by local metasomatic processes that operate shortly before the volcanic eruption. Hence, water abundances in minerals of Tok mantle xenoliths appear to represent a snapshot of water in the vicinity of the xenolith source regions. [ABSTRACT FROM AUTHOR]

The composition of a planet's core has important implications for the thermal and magmatic evolution of that planet. Here, we conducted carbon (C) solubility experiments on iron‐silicon (Fe‐Si) metal mixtures (up to 35 wt% [~52 atom%] Si) at 1 GPa and 800–1800°C to determine the carbon concentration at graphite saturation (CCGS) in metallic melt and crystalline metal with varying proportions of Fe and Si to constrain the C content of Mercury's core. Our results, combined with those in the literature, show that composition is the major controlling factor for carbon solubility in Fe‐rich metal with minimal effects from temperature and pressure. Moreover, there is a strong anticorrelation between the abundances of carbon and silicon in iron‐rich metallic systems. Based on the previous estimates of <1–25 wt% Si in Mercury's core, our results indicate that a carbon‐saturated Mercurian core has 0.5–6.4 wt% C, with 6.4 wt% C corresponding to an Si‐free, Fe core and 0.5 wt% C corresponding to an Fe‐rich core with 25 wt% Si. The upper end of estimated FeO abundances in the mantle (up to 2.2 wt%) are consistent with a core that has <1 wt% Si and up to 6.4 wt% C, which would imply that bulk Mercury has a superchondritic Fe/Si ratio. However, the lower end of estimated FeO (≤0.05 wt%) supports CB chondrite‐like bulk compositions of Mercury with core Si abundances in the range of 5–18.5 wt% and C abundances in the range of 0.8–4.0 wt%. Plain Language Summary: The composition of a planet's core can provide clues as to how the planet has changed over time. In this study, we conducted experiments at high pressures and temperatures to investigate potential carbon and silicon abundances in the core of Mercury. We utilized a variety of iron‐silicon metal mixtures (up to 35 wt% silicon) and graphite capsules in order to examine the concentration of carbon in metallic melts and crystalline metals at graphite saturation with the intention of constraining the carbon and silicon content of Mercury's core. Combining the results of this study with those in the literature, we found that composition is the major controlling factor of carbon solubility in silicon‐bearing, iron‐rich metal, with minimal effects from temperature. More importantly, our results showed a strong anticorrelation between the abundances of carbon and silicon in iron‐rich metallic systems. Since Mercury may have formed in a region of the solar system with less oxygen available, it is likely that some silicon partitioned into Mercury's core as silicon becomes more siderophile under reducing conditions. These findings, when combined with other elemental data, can be used to place constraints on the bulk composition of Mercury, which could help to constrain its origin. Key Points: Composition is the main control of carbon concentration at graphite saturation in Fe‐rich metal, with minimal effects from temperature and pressureMercury requires ≥27 wt% Si and ≤0.5 wt% C in its core if it has a bulk EH chondritic compositionMercury requires 5–18.5 wt% Si and 0.8–4.0 wt% C in its core if it has a bulk CB chondritic composition [ABSTRACT FROM AUTHOR]

Electron probe and ion probe are the two most used instruments for in situ analysis of halogens in geological materials. The comparison of these two methods on widely distributed glass standards (example: MPI-DING glasses, Jochum et al., G-cubed, 2006) provides a basis for establishing laboratory method, independent geochemical data sets for these elements. We report analyses of F, S, and Cl concentrations in three geological glass samples (EPMA) and 10 referenced standards (EPMA and SIMS). Furthermore, F and Cl absolute abundances have been determined independently for three of the standards (KL2-G, ATHO-G, and KE12), via heavy ion elastic recoil detection analysis (HIERDA), to certify the accuracy of the cross-calibration EPMA-SIMS. The detection limits for EPMA are a 150 mg·g-1 for F, 20 mg·g-1 for S and Cl, and for SIMS < 48 mg·g-1 for F, < 3 mg·g-1 for S, and <19 mg·g-1 for Cl. On SiO2-rich glass-standards, F and Cl measurements by HIERDA highlight a weak matrix effect during SIMS analysis of F and Cl. With the HIERDA independently measured value, we therefore propose an alternative calibration function to empirically correct this matrix effect on the SIMS measurements of F, S, and Cl. [ABSTRACT FROM AUTHOR]

The three-dimensional (3-D) electrical structure of the upper-mantle was used to examine the deep origins of and relationship among the Cenozoic volcanoes located in Northeast China (NEC). High-quality, long-period magnetotelluric (LMT) full-impedance tensor data were collected in NEC and subjected to 3-D Gauss-Newton inversion in order to construct a resistivity model. The resulting model reveals the presence of multiple localized low-resistivity anomalies (LRAs) within the high-resistance lithosphere beneath NEC. These LRAs partially coincide with Cenozoic volcanoes on the surface. Three LRAs that form a larger, annular LRA were observed in the deep upper mantle beneath the Songliao Basin, whereas vein-like LRAs were found in the asthenosphere that connect the lithosphere and deep upper mantle. Petrophysical analyses suggest that the LRAs may have been caused by fluid-induced melting. Based on our electrical model, we propose that, following dehydration of the subducted Western Pacific slab into the mantle transition zone (MTZ) beneath NEC, the released water migrated upward and caused partial melting at the top of the MTZ beneath the Songliao Basin. Under the effect of buoyancy, the melted mantle formed a thermal upwelling that caused melting of asthenosphere before diapiring at the base of the dry lithosphere. The magma then penetrated structural boundaries (such as thinner, weaker, or activated suture zones) and finally reached the Earth's surface. This melting and upwelling of hot mantle materials may have resulted in large-scale volcanism in the region throughout the Cenozoic, including the eruption of Changbai Mountain and Halaha Volcanoes. Our results suggest that the Cenozoic NEC volcanoes may all share a similar mode of genesis, and probably originated from the annular LRA in the deep upper mantle. [ABSTRACT FROM AUTHOR]

High‐temperature ionic conductivity in olivine single crystals has been measured in the [100], [010], and [001] crystallographic orientations as a function of pressure from 2 to 10 GPa, temperature from 1450 to 2180 K, and H2O content from 20 to 580 wt. ppm using multianvil presses with in situ impedance analyses. The experimental results yield an activation energy, activation volume, and H2O content exponent of 250–405 kJ/mol, 3.2–5.3 cm3/mol, and 1.3 ± 0.2, respectively, for the high‐temperature ionic conduction regime. Olivine ionic conductivity has negative pressure and positive temperature dependences and is significantly enhanced by H2O incorporation. The [001] direction is more conductive than the [100] and [010] directions. The H2O‐enhanced ionic conductivity may contribute significantly to the electrical conductivity profile in the asthenosphere, especially in the regions under relatively high‐temperature and low‐pressure conditions. Key Points: Pressure, temperature, and water content dependences of olivine ionic conductivity are obtainedOlivine ionic conductivity is dramatically enhanced by water incorporationOlivine ionic conductivity may contribute significantly to the bulk conductivity of olivine in the asthenosphere [ABSTRACT FROM AUTHOR]

Bastnaesite (Ce0.50La0.25Nd0.20Pr0.05)CO3F is an interesting pattern family of (CO3)2− and F− co-existing phases, which is a meaningful sample to study the influence of multiple volatiles on minerals. Thermal stability of bastnaesite has been investigated by thermogravimetric experiment and in situ high-temperature Raman. The results demonstrate that bastnaesite undergoes a decarbonization transition at above 673 K. The isobaric-mode Grüneisen parameters range from 0.04 to 2.28. The compressibility of bastnaesite has been investigated by synchrotron radiation X-ray diffraction and Raman spectroscopy combined with diamond anvil cells up to 19.2 GPa at room temperature. Isothermal pressure–volume relationship of bastnaesite is fitted to the second-order Birch–Murnaghan equation of state with V0 = 430.87(3) Å3, K0 = 118.35(1) GPa. Its axial compressibility presents anisotropic, attributed to the rigid (CO3)2− group parallel to c-axis. Its isothermal-mode Grüneisen parameters and intrinsic anharmonic-mode parameters range from 0.23 to 1.91 and− 3.5 × 10−5 K−1 to 0.82 × 10−5 K−1, respectively. The presence of F− can largely enhance the thermal stability and incompressibility of minerals. [ABSTRACT FROM AUTHOR]

Water influences geodynamic processes such as melting, deformation and rheology, yet its distribution in the oceanic upper mantle is primarily known indirectly from melt inclusions and glasses of erupted mantle melts (i.e. mid-ocean ridge and ocean island basalts). To better constrain the mechanisms influencing the distribution of H2O in the mantle, particularly regarding the role of metasomatism, we analyzed 15 peridotite xenoliths from Savai'i and two dunite xenoliths from Ta'ū (Samoa) for structural H2O (by polarized Fourier transform infrared spectroscopy), and major and trace element concentrations. Clinopyroxenes from the Ta'ū dunites show trace element concentrations consistent with equilibration with their host lavas, but lower H2O contents than expected. Savai'i peridotites are highly depleted harzburgites (melt depletion ≥17 %). They show strong evidence of transient metasomatism by both carbonatite and silicate melts, with highly variable Ti and Zr depletions and light rare earth element enrichments. However, despite metasomatism the H2O concentrations in olivines (0 − 4 ppm H2O) and orthopyroxenes (17 − 89 ppm H2O) are among the lowest reported in oceanic xenoliths, but higher than expected for the estimated degree of depletion. In general, H2O concentrations vary less than those of other incompatible trace elements in these samples. Transects across mineral grains show generally homogeneous distributions of H2O, indicating no significant H2O loss or gain during ascent. Raman spectroscopy on inclusions in minerals shows the presence of CO2 but an absence of molecular H2O. This agrees with the absence of H2O concentration variations between inclusion-rich and -poor domains in minerals. The above data can be explained by transient metasomatism along grain boundaries, now recorded as planes of inclusions within annealed grains. Fast diffusion of hydrogen (but not lithophile elements) from the inclusions into the host mineral phase will simultaneously enrich H2O contents across the grain and lower them in the inclusion-rich domains. The result is highly variable metasomatism recorded in lithophile elements, with smaller magnitude H2O variations that are decoupled from lithophile element metasomatism. Comparison with xenoliths from Hawai'i shows that evidence for metasomatism from lithophile elements alone does not imply rehydration of the oceanic lithosphere. Instead, H2O concentrations depend on the overall amount of H2O added to the lithosphere through metasomatism, and the proximity of sampled material to areas of melt infiltration in the lithosphere. [ABSTRACT FROM AUTHOR]

Dredging and disposal of sediments onto land sites is a common practice in urban and industrial areas that can present environmental and health risks when the sediments contain metallic elements. The aim of this study was to characterise and study the environmental and toxicological availability of Cd and Pb in anthroposols from dredged river sediments. To do this, 67 surface samples spread over 12 sediment disposal sites in northern France were studied. The results showed substantial heterogeneity for this matrix in terms of physicochemical parameters and contamination degree; however, ascending hierarchical clustering made it possible to classify the samples into eight groups. For each group, the mobile fraction of Cd and Pb was studied using single EDTA extraction, solid-phase distribution was analysed with sequential extractions and toxicological availability was assessed with the oral bioaccessibility test. The results showed that (i) Cd had a higher environmental and toxicological availability than Pb; (ii) this availability depends on the physicochemical characteristics of the matrix; and (iii) it is necessary to take into account the environmental and toxicological availability of contaminants when requalifying these sites in order to propose appropriate management measures. In the first years after sediment disposal, it would appear that the environmental and toxicological availability of Cd and Pb increased (from 52.5 to 71.8% and from 28.9 to 48.9%, respectively, by using EDTA and from 50.2 to 68.5% for Cd with the bioaccessibility test). Further studies would therefore be required to confirm this trend and understand the mechanisms involved. [ABSTRACT FROM AUTHOR]

The generation of strongly potassic melts in the mantle requires the presence of phlogopite in the melting assemblage, while isotopic and trace element analyses of ultrapotassic rocks frequently indicate the involvement of subducted crustal lithologies in the source. However, phlogopite-free experiments that focus on melting of sedimentary rocks and subsequent hybridization with mantle rocks at pressures of 1-3 GPa have not successfully produced melts with K2O >5 wt%-6 wt%, while ultrapotassic igneous rocks reach up to 12 wt% K2O. Accordingly, a two-stage process that enriches K2O and increases K/Na in intermediary assemblages in the source prior to ultrapotassic magmatism seems likely. Here, we simulate this two-stage formation of ultrapotassic magmas using an experimental approach that involves re-melting of parts of an experimental product in a second experiment. In the first stage, reaction experiments containing layered sediment and dunite produced a modally metasomatized reaction zone at the border of a depleted peridotite. For the second-stage experiment, the metasomatized dunite was separated from the residue of the sedimentary rock and transferred to a smaller capsule, and melts were produced with 8 wt%-8.5 wt% K2O and K/Na of 6-7. This is the first time that extremely K-enriched ultrapotassic melts have been generated experimentally from sediments at low pressure applicable to a post-collisional setting. [ABSTRACT FROM AUTHOR]

Data from Mariner 10, MESSENGER, and ground-based telescopic observations have facilitated great advancements towards understanding the geochemistry, geology, internal structure, exosphere, and magnetosphere of Mercury. However, there are critical science questions that can be only addressed via examination of a sample in Earth-based laboratories, where numerous highly sensitive analytical measurements are possible. Collecting a sample from the surface of Mercury and bringing it to Earth for in-depth analysis would allow for transformative Solar System science to be conducted, examining aspects of our Solar System such as the evolution of the protoplanetary disk, space weathering on airless bodies, the geochemical behavior of elements at extreme conditions, and the origin and distribution of volatiles across the terrestrial planets. Furthermore, our knowledge of Mercury's differentiation and geochemical processes, chronology and geologic evolution, tectonism and geomechanical properties, and past and ongoing magnetism would be greatly advanced via analysis of a sample from Mercury. Although there are ample challenges and knowledge gaps associated with sample return from Mercury in terms of both spacecraft requirements and material requirements for curatorial facilities, a sample from the planet would be an invaluable scientific resource for generations to come, enabling the most sophisticated measurements to be brought to bear for decades and helping to truly unlock the mysteries of our Solar System. [ABSTRACT FROM AUTHOR]

Mars lacks an internally generated magnetic field today. Crustal remanent magnetism and meteorites indicate that a dynamo existed after accretion but died roughly four billion years ago. Standard models rely on core/mantle heat flow dropping below the adiabatic limit for thermal convection in the core. However, rapid core cooling after the Noachian is favored instead to produce long‐lived mantle plumes and magmatism at volcanic provinces such as Tharsis and Elysium. Hydrogenation of the core could resolve this apparent contradiction by impeding the dynamo while core/mantle heat flow is superadiabatic. Here we present parameterized models for the rate at which mantle convection delivers hydrogen into the core. Our models suggest that most of the water that the mantle initially contained was effectively lost to the core. We predict that the mantle became increasingly ironrich over time and a stratified layer awaits detection in the uppermost core—analogous to the E′ layer atop Earth's core but likely thicker than alternative sources of stratification in the Martian core such as iron snow. Entraining buoyant, hydrogen‐rich fluid downward in the core subtracts gravitational energy from the total dissipation budget for the dynamo. The calculated fluxes of hydrogen are high enough to potentially reduce the lifetime of the dynamo by several hundred million years or longer relative to conventional model predictions. Future work should address the complicated interactions between the stratified, hydrogen‐rich layer and convection in the underlying core. Plain Language Summary: The demise of the Martian magnetic field roughly four billion years ago is one of the greatest mysteries in the solar system. Many scientists believe that the temperature of the core is to blame. Producing the magnetic field requires a dynamo arising from convection in the core—like a boiling pot on a stove but with molten iron instead of water. If the core started at a certain initial temperature, then its predicted cooling history agrees with ages of magnetized crust. However, models that attempt to explain the longevity of observed volcanism prefer an even hotter core. Here we study the amount of hydrogen that may enter the core through chemical reactions with minerals above the core that contain water. We found that the core may now contain most of the hydrogen that was initially located in the mantle. The predicted rates of hydrogen transport may strongly affect the energy budget for convection and the dynamo. Hydrogenation could never suppress a dynamo in other planets because they are too small (Mercury) or too large (Earth) for minerals containing significant amounts of water to contact the core. We suggest tests of our model for future laboratory experiments, simulations, and spacecraft missions. Key Points: Mantle convection may deliver most of the primordial hydrogen from the mantle to the core via redox reaction at the core/mantle boundaryHydrogen injected into the core could form a stratified layer and perhaps hinder the dynamo by sapping gravitational energy from convectionThe NASA InSight mission or future geophysical platforms should provide key constraints on models of core hydrogenation [ABSTRACT FROM AUTHOR]

We investigate the inclusions hosted in peritectic garnet from metapelitic migmatites of the Kinzigite Formation (Ivrea Zone, NW Italy) to evaluate the starting composition of the anatectic melt and fluid regime during anatexis throughout the upper amphibolite facies, transition, and granulite facies zones. Inclusions have negative crystal shapes, sizes from 2 to 10 μm and are regularly distributed in the core of the garnet. Microstructural and micro‐Raman investigations indicate the presence of two types of inclusions: crystallized silicate melt inclusions (i.e., nanogranitoids, NI), and fluid inclusions (FI). Microstructural evidence suggests that FI and NI coexist in the same cluster and are primary (i.e., were trapped simultaneously during garnet growth). FI have similar compositions in the three zones and comprise variable proportions of CO2, CH4, and N2, commonly with siderite, pyrophyllite, and kaolinite, suggesting a COHN composition of the trapped fluid. The mineral assemblage in the NI contains K‐feldspar, plagioclase, quartz, biotite, muscovite, chlorite, graphite and, rarely, calcite. Polymorphs such as kumdykolite, cristobalite, tridymite, and less commonly kokchetavite, were also found. Rehomogenized NI from the different zones show that all the melts are leucogranitic but have slightly different compositions. In samples from the upper amphibolite facies, melts are less mafic (FeO + MgO = 2.0–3.4 wt%), contain 860–1700 ppm CO2 and reach the highest H2O contents (6.5–10 wt%). In the transition zone melts have intermediate H2O (4.8–8.5 wt%), CO2 (457–1534 ppm) and maficity (FeO + MgO = 2.3–3.9 wt%). In contrast, melts at granulite facies reach highest CaO, FeO + MgO (3.2–4.7 wt%), and CO2 (up to 2,400 ppm), with H2O contents comparable (5.4–8.3 wt%) to the other two zones. Our results represent the first clear evidence for carbonic fluid‐present melting in the Ivrea Zone. Anatexis of metapelites occurred through muscovite and biotite breakdown melting in the presence of a COH fluid, in a situation of fluid–melt immiscibility. The fluid is assumed to have been internally derived, produced initially by devolatilization of hydrous silicates in the graphitic protolith, then as a result of oxidation of carbon by consumption of Fe3+‐bearing biotite during melting. Variations in the compositions of the melts are interpreted to result from higher T of melting. The H2O contents of the melts throughout the three zones are higher than usually assumed for initial H2O contents of anatectic melts. The CO2 contents are highest at granulite facies, and show that carbon‐contents of crustal magmas are not negligible at high T. The activity of H2O of the fluid dissolved in granitic melts decreases with increasing metamorphic grade. Carbonic fluid‐present melting of the deep continental crust represents, together with hydrate‐breakdown melting reactions, an important process in the origin of crustal anatectic granitoids. [ABSTRACT FROM AUTHOR]

Three parameters: temperature, hydrogen content, and the presence of partial melt, are the dominant controls on the rheology of the convecting upper mantle. As such, they determine the dynamics that control plate tectonics and continental evolution. Since hydrogen depresses the peridotite solidus temperature, these parameters are strongly linked petrologically. We have developed a genetic algorithm code to statistically assess the likelihood that a section of upper mantle contains partial melt. This code uses magnetotelluric observations and petrological constraints on composition and solidus temperatures and allows for uncertainties in the geotherm and the electrical conductivity structure. We have applied this code to the convecting upper mantle beneath (1) a stable continent (the Superior Craton); (2) a hot spot (Tristan da Cunha); (3) stable, old oceanic lithosphere (the northwest Pacific Ocean); and (4) young oceanic lithosphere (adjacent to the East Pacific Rise). Results show that the volume of melt in the convecting upper mantle is heterogeneous. The highest melt proportions are beneath the hot spot while little to no melt is required in the other regions. All regions show low water contents (generally <50 wt ppm in olivine) in the shallow convecting upper mantle, making it unlikely that water causes a large or sharp viscosity contrast between the lithosphere and the convecting mantle. Results differ significantly for different experimental olivine hydrogen conductivity models, highlighting the importance of reconciling these experimental constraints. Plain Language Summary: Plate tectonics occurs because the strong tectonic plates sit on underlying weaker and softer mantle that flows over geological timescales. We do not fully understand why this deeper mantle is weak—the two main contenders are that a small part of it is molten or that it contains nominal amounts of the element hydrogen. The electrical conductivity of the mantle is increased both by the presence of molten rock and by hydrogen, so when we interpret conductivity data, it is difficult to distinguish between these two interpretations. We have written a new code to help this. It analyzes whether the conductivity of the mantle could only be explained by the presence of molten rock, whether it could only be explained by large hydrogen contents, or whether it could be explained by either. Our results show that the distribution of partially molten rock is very uneven: Most lies beneath hot spot volcanic islands, while there is no need for molten rock to be present beneath old continents or old parts of the ocean. Beneath young parts of the ocean, the electrical conductivities could be explained by either a small amount of molten rock or by large hydrogen contents. Key Points: A genetic algorithm scheme statistically assesses the likelihood that the upper mantle contains melt from magnetotelluric dataMelt distribution is heterogeneous, with the most likelihood for melt beneath hot spots and the least beneath cratons and old oceansUncertainties in experimental constraints lead to substantially different results [ABSTRACT FROM AUTHOR]

We analyze peridotites from a wide range of tectonic settings to investigate relationships between olivine crystallographic preferred orientation (CPO) and deformation conditions in naturally deformed rocks. These samples preserve the five olivine CPO types (A‐ through E‐type) that rock deformation experiments have suggested are controlled by water content, temperature, stress magnitude, and pressure. The naturally deformed specimens newly investigated here (65 samples) and compiled from an extensive literature review (445 samples) reveal that these factors may matter less than deformation history and/or geometry. Some trends support those predicted by experimentally determined parametric dependence, but several observations disagree—namely, that all CPO types are able to form at very low water contents and stresses and that there is no clear relationship between water content and CPO type. This implies that at the low stresses typical of deformation in the mantle, CPO type more commonly varies as a function of strain geometry. Because olivine CPO is primarily responsible for seismic anisotropy in the upper mantle, the results of this study have several implications. These include (1) the many olivine CPO types recorded in samples from individual localities may explain some of the complex seismic anisotropy patterns observed in the continental mantle, and (2) B‐type CPO—where olivine's "fast axes" align perpendicular to flow direction—occurs under many more conditions than traditionally thought. This study highlights the need for more experiments and the difficulty in using olivine CPO in naturally deformed peridotites to infer deformation conditions. Key Points: Natural samples reveal complex relationships between olivine CPO and deformation conditionsOlivine CPO types vary more often with strain geometry than water and stress in studied peridotitesB‐type olivine CPO can form under a wide range of temperatures and at low stresses and water contents [ABSTRACT FROM AUTHOR]

Fingerprinting hydrogen storage sites in olivine at high temperature and high pressure is fundamental to understand water distribution and its impact on the upper mantle. We carried out in situ high-temperature and high-pressure IR spectroscopic investigations on hydrogen storage sites in the natural olivine and synthetic Fe-free forsterite. Based on in situ observations of hydrogen in both the natural olivine and synthetic Fe-free forsterite at high temperatures and high pressures, we find that hydrogen does not transfer between storage sites with increasing temperature, but displays disordering at temperatures over 600 °C. In contrast, pressure can induce re-configuration of hydrogen storage sites corresponding to the 3610 and 3579 cm–1 bands. Hydrogen storage sites also exhibit disordering at high pressure. In addition, the dehydrogenation experiments of the natural olivine indicate interacts of hydrogen storage sites. Protons released from titanium-clinohumite defects move to pure Si vacancies, and also to Mg vacancies coupling with trivalent cations. This study is the first attempt to fingerprint hydrogen storage sites in olivine at high temperature and high pressure using in situ IR spectroscopy. The implications of the temperature- and pressure-induced disordering and re-configuration of hydrogen storage sites are discussed. The disordering and re-configuration of hydrogen storage sites at high temperature and high pressure favor better understanding of the water effects on physical properties of olivine. The interactions of hydrogen storage sites during dehydrogenation warn that some hydrogen if observed in dehydrated mantle-derived samples may not be original and also make hydrogen diffusivity complex. [ABSTRACT FROM AUTHOR]

Comparison between geophysical observations and laboratory measurements yields contradicting estimations of the melt fraction for the partially molten regions of the Earth, highlighting potential disagreements between laboratory-based electrical conductivity and seismic wave velocity measurement techniques. In this study, we performed simultaneous acoustic wave velocity and electrical conductivity measurements on a simplified partial melt analogue (olivine + mid oceanic ridge basalt, MORB) at 2.5 GPa and up to 1650 K. We aim to investigate the effect of ongoing textural modification of partially molten peridotite analog on both electrical conductivity and sound wave velocity. Acoustic wave velocity (Vp and Vs) and EC are measured on an identical sample presenting the same melt texture, temperature gradient, stress field and chemical impurities. We observe a sharp decrease of acoustic wave velocities and increase of electrical conductivity in response to melting of MORB component. At constant temperature of 1650 K, electrical conductivity gradually increases, whereas acoustic velocities remain relatively constant. While the total MORB components melt instantaneously above the melting temperature, the melt interconnectivity and the melt distribution should evolve with time, affecting the electrical conduction. Consequently, our experimental observations suggest that acoustic velocities respond spontaneously to the melt volume fraction for melt with high wetting properties, whereas electrical conduction is significantly affected by subsequent melt texture modifications. We find that acoustic velocity measurements are thus better suited to the determination of the melt fraction of a partially molten sample at the laboratory time scale (~ h). Based on our estimations, the reduced Vs velocity in the major part of the low velocity zone away from spreading ridges can be explained by 0.3–0.8 vol% volatile-bearing melt and the high Vp/Vs ratio obtained for these melt fractions (1.82–1.87) are compatible with geophysical observations. [ABSTRACT FROM AUTHOR]

Melting experiments were performed on the Fe‐C‐H system to 127 GPa in a laser‐heated diamond anvil cell. On the basis of in situ and ex situ sample characterizations, we found that the solubility of carbon in liquid Fe correlates inversely with hydrogen concentration at ~60 GPa and ~3500 K, indicating that liquid Fe preferentially incorporates hydrogen rather than carbon under conditions with abundant C and H. While large amounts of both C and H may have been delivered to the growing Earth, C‐poor/H‐rich metals were likely added to the protocore in the late stages of core formation. We also obtained a melting curve of FeHx (x > 1) far beyond the pressure range in earlier determinations. Its liquidus temperature was found to be 2380 K at 135 GPa, lower than those of Fe alloyed with the other possible core light elements. Relatively low core temperature is thus supported by the presence of hydrogen. Plain Language Summary: Both carbon and hydrogen are possible major light elements in the core but estimation of their abundance in the core as well as in the bulk Earth is difficult because of their high volatility. In addition, the property of hydrogen‐bearing iron alloys has been the least studied. Here we performed melting experiments on Fe‐C‐H to 127 GPa, close to the pressure at the top of the Earth's core. Our main finding is that hydrogen limits the solubility of carbon in liquid Fe; the carbon content correlates inversely with hydrogen concentration in molten Fe coexisting with diamonds at ~60 GPa and ~3500 K. Recent planet formation theories suggest that large amounts of C and H were delivered to the growing Earth. In the late stages of core formation, liquid metals preferentially incorporating hydrogen rather than carbon may have added to the protocore. We also found that hydrogen decreases the melting temperature of Fe remarkably. The melting temperature of FeHx (x > 1) is only about 2380 K at the core‐mantle boundary; lower than those of Fe‐Fe3S eutectic and Fe alloyed with the other possible core light elements. Key Points: Melting experiments on the Fe‐C‐H system were performed to 127 GPaHydrogen limits the solubility of carbon in liquid ironMelting temperature of FeHx (x > 1) is about 2380 K at 135 GPa, lower than those of Fe alloyed with the other possible core light elements [ABSTRACT FROM AUTHOR]