Melt H2O Research Articles

Molten-chlorides assisted rapid preparation and crystallinity-irrelevant properties of nanostructured LiCoO2 as lithium-ion battery cathodes

In this paper, the 850 °C molten-chlorides (NaCl-KCl, eutectic point ∼657 °C) assisted reaction of Co3O4 (melting point ∼895 °C) with LiOH⋅H2O (melting point ∼462 °C) is adopted for the precursor shape-replicated construction of nanostructured LiCoO2, focusing on the rapid formation mechanism and crystallization-irrelevant properties of phase-pure LiCoO2 for Li-ion battery (LIB) cathodes. Temperature−/time-dependent crystallization shows that, after the heterogeneous nucleation of LiCoO2 at 660 °C, the complete consumption of Co3O4 occurs at 850 °C within 10 min and the building block of each of the finally resulting 850 °C/8-h LiCoO2 microspheres has been endowed with a (003)-manifest crystal plane. By comparison, it is due to the complete consumption of Li-insulating Co3O4, not to the increase of LiCoO2 crystallinity, that explains the high electrochemical properties of these phase-pure samples. Especially, cycling stabilities of the 850 °C/10-min and 850 °C/8-h LiCoO2 are close to each other, but each of them is much better than those of the chlorides-absent counterparts obtained at the node of 850 °C/8-h. These, together with the approximate rate capabilities of these chlorides-present LiCoO2, implies an applicable approach of the molten-salt method to the rapid construction of nanostructured LiCoO2 for high-performance LIB cathodes.

High heat producing granites and prolonged extraction of tungsten and tin from melts

The granites associated with world–class W and Sn deposits generally have high concentrations of U, Th, and K and can be classified as high heat producing (HHP) granites (>5 μW m−3) because of high radiogenic heat production, but how long radiogenic heat can prolong the suprasolidus lifetime of magmas and whether radiogenic heat exerts an impact on W and Sn mineralization is poorly understood. To answer these questions, finite element numerical modeling was established to link magma cooling by heat conduction with diffusion of W, Sn, and H2O from silicate melts to coexisting aqueous fluids before the solidus is reached. The magma in the models is emplaced to a depth of 5 km and its size (vertical thickness of 4–5 km and horizontal length of 20 km) is constrained by the granites associated with world–class W and Sn deposits. Fluid convection was not considered in the models. The sensitivity analysis and comparison results suggest that the suprasolidus lifetimes of HHP magmas are positively correlated with the heat production and magma thickness and negatively correlated with the solidus temperatures and the thermal conductivity of host rocks. Average radiogenic heat of 5–10 μW m−3, together with decreased solidus temperatures due to magmatic differentiation and a moderate thermal conductivity of host rocks, can prolong the suprasolidus lifetime of HHP magmas by 49–427 ka (1 Ma = 1000 ka), corresponding to 11–85% of the suprasolidus lifetime of equally sized magmas with normal radiogenic heat (2 μW m−3). From the available gravity modeling data, over half of the granites associated with world–class W and Sn deposits are at least 1 km thicker than the values calculated from the empirical power–law equation, and the modeling results indicate that an increase of 500–1000 m in magma thickness prolongs the suprasolidus lifetimes of HHP magmas (5 μW m−3) by 50–74%. During magma cooling before solidus is reached, the diffusion of W and Sn is at least several orders of magnitude slower than that of H2O in hydrous melts; thus, the equilibrium partitioning of these two metals between silicate melts and coexisting aqueous fluids is not reached, and the metal diffusion from melts is a rate-limiting step. The prolongation of the suprasolidus lifetimes by radiogenic heat and decreased solidus temperatures can allow extraction of 17–95% more W and Sn from silicate melts before the solidus is reached and increase the possibility of producing W and Sn mineralization at later stages. Therefore, the coexistence of HHP granites and world–class W and Sn deposits is not accidental.

H2O-Controlled Eruptive Filtering on the Bimodality of Continental Volcanism Across Tectonic Settings

Abstract The contemporary basaltic and rhyolitic volcanism with a dearth of intermediate compositions creates a compositional gap (‘Daly gap’), which is known to be pronounced in continental rifts/hotspots but absent in continental arcs. The intrinsic mechanism(s) producing the Daly gap remain poorly understood. Similar bimodal spectra recorded in melt inclusions from continental rifts/hotspots and arcs suggest that similar processes modulate the bulk composition of erupted magmas. A compiled data set of melt inclusion composition, phenocryst fraction, pre-eruptive temperature and melt H2O content enables precise calculations of melt viscosities and bulk magma viscosities for >100 eruptions of global volcanoes in various tectonic settings. Analyses of the data set suggest lower viscosities of rhyolitic melts in arcs than in rifts/hotspots (~104.5 ± 0.2 versus ~105.5 ± 0.2 Pa·s, respectively), at comparable temperatures, because of ~1.5 wt % higher melt H2O contents in arcs. Combining numerical constraints on ascent dynamics and data set observations, our study defines an eruption threshold of ~106.0 ± 0.3 Pa·s at the base of a volcanic conduit rooted in the subvolcanic reservoir. The lower viscosities of rhyolitic melts in arcs facilitate stirring/re-homogenization of upper crustal reservoirs upon recharge and accommodation of more phenocrysts in erupted products, leading to the common appearance of crystal-rich (30–50%) andesites and dacites (with rhyolitic interstitial melts) with mixing signatures in magmatic provinces of continental arcs. In contrast, the lower mixing efficiency and eruptibility of the more viscous magmas present in continental rifts/hotspots lead to preferential eruption of crystal-poor (<~30%) rhyolites, enhancing compositional bimodality in the erupted records. This H2O-controlled eruptive filter modulates the presence versus absence of the Daly gap and is key to the distinct differentiation patterns across tectonic settings.

Geology of the Liuyuan Complex, NW China: A Permian back-arc basin ophiolite at the southern edge of the Central Asian orogenic belt

Located in the southern margin of the Central Asian orogenic belt, the stratigraphy and tectonic setting of the mafic 290−280 Ma Liuyuan Complex have been controversial for decades, with workers arguing for a forearc ophiolite or a continental rift setting. Here, we present the results of a detailed field study, where the Liuyuan Complex was subdivided into troctolite, melatroctolite, layered gabbro, varitextured olivine gabbro, hornblende gabbro, plagiogranite, sheeted dike, and mafic tectonite, in addition to previously identified and studied basalt and chert. All contacts between the igneous facies are intrusive, with gabbroic rocks separated from the overlying basalt by a well-developed and laterally continuous sheeted dike complex. Based on their geochemical affinities, two groups of basalt were identified: group I (low-TiO2) and group II (high-TiO2). A modeled liquid line of descent, assuming perfect mineral fractionation, with a liquidus temperature of 1212 °C, pressure of 1 kbar, fO2 at the quartz-fayalite-magnetite (QFM) buffer, and initial melt H2O of 0.5 wt%, provides an excellent fit to group I lavas, with group II basalts interpreted as having formed from a distinct arc source. The stratigraphy, extended trace-element patterns, and tectonic fingerprinting of the lavas suggest the Liuyuan Complex formed as an ophiolite in a fast-spreading back-arc basin, a setting inconsistent with previously proposed tectonic models for the southern Central Asian orogenic belt. We expand on a tectonic model that proposes the Liuyuan Complex formed as a back-arc to the recently identified Ganquan arc. The back-arc basin was then consumed in a north-dipping subduction zone beneath the active margin of composite Siberia. The magmatic center of this arc migrated southward, likely caused by slab roll-back, with the Liuyuan Complex becoming the basement of an arc. Exhumation of the Liuyuan Complex took place by 267 Ma, as constrained by the age of a subaerial dacite that unconformably overlies the basalts of the Liuyuan Complex.

UNDERSTANDING Cu DEFICIENCY AND Mo ENRICHMENT IN THE JURASSIC ZHANGGUANGCAI-LESSER XING’AN CONTINENTAL ARC (NE CHINA): INSIGHTS FROM THE LUMING PORPHYRY MO DEPOSIT

Abstract Continental arcs are favorable sites for porphyry Cu ± Mo deposits. In contrast, the Jurassic Zhangguangcai-Lesser Xing’an continental arc, northeastern China, hosts numerous porphyry Mo deposits with only minor total Cu endowment. The reasons for this remain elusive. Here, we address the issue by tracking the origin and evolution of a long-lived (ca. 12 m.y.) magmatic suite associated with one of the largest Mo deposits in the Zhangguangcai-Lesser Xing’an range continental arc—the Luming porphyry Mo deposit. In combination with previous geochronological data, our results indicate that the pre- (187.5–186.5 Ma) and syn-ore (178.6–175.6 Ma) intrusions at Luming represent separate magma batches from isotopically similar parental magmas with the signature of subduction-metasomatized mantle-derived magmas mixed with crustal melts. The Sr/Y, La/YbN, Dy/YbN, and Eu/Eu* values, together with fO2 and apatite S and Cl concentrations of the syn-ore intrusions, however, are systematically higher than pre-ore intrusions. These data indicate that there is a distinct change in magma chemistry during the period of magmatism quiescence between the pre- and syn-ore magmatism. The marked change in magma chemistry is coincident with an episode of major compression and crustal thickening in the Zhangguangcai-Lesser Xing’an range. We, therefore, interpret that the chemical changes most likely reflect a deepening of the locus of lower crustal magma evolution, linked to increased crustal thickness and/or melt H2O contents accompanying an increase in orogenic stress. Considering the tectonic setting, magmatic evolution in the deep crust, emplacement depth, fractionation degree, and oxygen fugacity of the porphyry Mo-related intrusions at Luming, they are very similar to porphyry Cu deposits worldwide. Accordingly, we propose that the deficiency in Cu and enrichment in Mo of the porphyry deposits in the Zhangguangcai-Lesser Xing’an range most likely formed due to mantle-derived magmas interacting with reduced crustal materials or melts in the deep crust. This resulted in substantial sequestration of Cu and S, decreasing porphyry Cu potential. Such an inference is supported by the distinctly lower S and Cl concentrations of the Mo-related intrusions in the Zhangguangcai-Lesser Xing’an range compared to those associated with porphyry Cu deposits. Our results confirm the fundamental role of increasing compressive stress, crustal thickening, and transcrustal petrologic processes in the formation of porphyry deposits and highlight the role of crustal components in modulating the Mo/Cu ratio of porphyry deposits in a continental arc setting. In addition, we tentatively propose that magmatic apatite SO3 and/or Cl contents can be used to discriminate porphyry Mo-related intrusions from those associated with porphyry Cu deposits in continental arcs.

Controls on determining the bulk water content of the Moon

AbstractThe Moon is much wetter than previously thought. The estimated bulk H2O concentrations based on the analyses of H2O in lunar materials show a wide range from 5 to 1650 ppm. To better constrain bulk H2O in the lunar magma ocean (LMO), we model LMO crystallization and vary DH (concentration of H2O in LMO mineral/concentration of H2O in melt), interstitial melt fraction, and initial LMO depth. We take the highest and lowest values of DH reported in the literature for the LMO minerals. We assess the bulk H2O content required in the initial magma ocean to satisfy two observational constraints: (1) H2O measured in plagioclase grains from ferroan anorthosites and (2) crustal mass from GRAIL. We find that the initial bulk LMO H2O that best explains the H2O content in crustal plagioclase is strongly dependent on DH rather than interstitial melt fractions or initial LMO depths, with a drier magma ocean (10 ppm H2O) being favored with higher DH and a wetter magma ocean (100–1000 ppm H2O) with lower DH. This underscores the importance of constraining DH specific to lunar conditions in future studies. We also demonstrate that crustal mass is not an effective hygrometer.

Petrogenesis and metal fertility of Yinzu pluton in the Daye district, eastern China: Insights from whole-rock and mineral (zircon, apatite and amphibolite) geochemistry

The Daye district in eastern China is featured by numerous granitoid intrusions of Early Cretaceous ages that intrude Paleozoic to Early Triassic marine carbonate and clastic rocks. Several dozen skarn Cu-Fe-Au deposits occur along the intrusive contact zones of the Echeng, Tieshan, Jinshandian, Lingxiang, Tongshankou and Tonglushan intrusions. However, no economic skarn mineralization has been recognized in other intrusions and whether or not these intrusions are metal fertile remain unresolved. In this paper, we use whole-rock and mineral (zircon, apatite and amphibole) geochemistry to provide significant new insights into the petrogenesis and metal fertility of the Yinzu granitoid pluton.The Yinzu pluton mainly consists of quartz diorite and diorite phases that have zircon U-Pb ages of 148.4 ± 1 Ma and 146.6 ± 1.6 Ma, respectively. Whole-rock Sr-Nd isotopic compositions ((87Sr/86Sr)i = 0.70635 to 0.70741; εNd(t) = −8.74 to −3.73) and zircon hafnium isotopes (εHf(t) = −9.1 to −4.8) overlap with values of the Cu-fertile Tongshankou and Tonglushan granitoids, implying a common enriched lithospheric mantle source. The whole-rock geochemical data suggest that both the diorite and quartz diorite have experienced variable degrees of fractional crystallization of olivine, amphibole, titanite and magnetite. The Ce4+/Ce3+ ratios (16–445) and oxygen fugacity (logfO2) calculated using trace element concentrations of zircon (ΔFMQ = +0.2 to +2.4) suggest that both intrusive phases crystalized from oxidized melts similar to Cu-fertile magmas in the world, with the quartz diorite being well comparable to the Tongshankou and Tonglushan granitoids. Based on available melt-apatite partitioning models, the estimated S and Cl contents for the magmas parental to the Yinzu pluton are akin to those of the Cu-fertile granitoids in the Daye district. Rocks of the Yinzu pluton display high apatite Sr/Y (0.38–3.01) and Eu/Eu* (0.35–0.71) ratios as well as high zircon Eu/Eu* (0.51–0.86) and 10000*(Eu/Eu*)/Y (2–27) ratios, indicating significant fractionation of amphibole with limited plagioclase fractionation and high magmatic water contents (>4 wt% H2O). This view is consistent with the calculated melt H2O content of 4.3–6.1 wt% based on the amphibole compositions.Collectively, results presented here indicate that magmas generating the Yinzu pluton are hydrous, oxidized and S-rich, characters similar to the Cu-fertile granitoids in Daye and elsewhere. Thus, the Yinzu pluton is considered to be Cu-(Au) fertile. This consideration is partially supported by occurrences of several vein-type Cu prospects within and disseminated Au ores in Silurian clastic sedimentary rocks immediately to the southeast of this pluton. Based on the regional metallogeny and results of this study, we suggest that the Yinzu pluton is a promising target of future Cu-(Au) exploration.

Highly differentiated felsic granites linked to Mo mineralization in the East Kunlun Orogenic Belt, NW China: Constrains from geochemistry, and Sr-Nd-Hf isotopes of the Duolongqiarou porphyry Mo deposit

The Mo deposits in the Kunlun-Qinling-Dabie orogen are mainly associated with porphyry or porphyry-skarn mineralisation in a collision or post-collision setting. However, collision-type Mo deposits that are related to granite and mineralization produced in magmatic systems remain poorly constrained. To better define the genetic relationship between the intrusions and Mo mineralization in collision setting, the geochronology, geochemistry, and Sr-Nd-Hf isotopes of the granodiorite and monzogranite in Duolongqiarou Mo deposit, East Kunlun Orogenic Belt (EKOB), NW China, are presented. Zircon U-Pb dating shows granodiorite and monzogranite ages of 237.6 ± 1.5 Ma and 236.8 ± 1.8 Ma, respectively, which is consistent with the molybdenite Re-Os weighted mean model age of 235.9 ± 1.4 Ma. This suggests that the granitic magma related to Mo mineralization at the Duolongqiarou formed during the Triassic (ca. 236 Ma). The ore-bearing monzogranites with high SiO2 contents (76.84–77.92 wt%) are peraluminous high-K calc-alkalic rocks, while the ore-barren granodiorites with low SiO2 contents (66.89–69.90 wt%) are metaluminous Na-rich calc-alkalic rocks. Both are enriched in large ion lithophile elements and light rare earth elements but depleted in high-field strength elements, which is characteristic of I-type granites. Ore-bearing and barren granites have similar εNd(t), εHf(t), and TDM2 age, indicating a similar magma source derived from partial melting of ancient Mesoproterozoic lower crustal components with involvement of mantle materials. The amphiboles of monzogranite show higher values of calculated pressures (average 122 MPa) and melt H2O content (average 5.7 wt%) than granodiorites, suggesting that monzogranites and granodiorites crystallized at different depths of the same magma chamber. Ore-bearing monzogranites show much lower contents of transition metals (e.g., Sc, V, and Cr), negative Eu anomalies (δEu = 0.32–0.46), and higher differentiation index values (94.52–96.92) compared to barren granodiorites. This suggests that high differentiation and fractionation promote Mo metal enrichment during magmatic evolution and subsequent formation of the magmatic-hydrothermal Duolongqiarou Mo deposit. The Duolongqiarou Mo deposit was formed in a collisional setting in response to the slab break-off of the EKOB Paleo-Tethys ocean. The results of this study combined with published data suggest that at least two generations of Mo polymetallic metallogenic events were observed in the Paleo-Tethys of the EKOB. This is very helpful to target porphyry Mo mineralization and guide regional exploration.

A thermodynamic model for sulfur content at sulfide saturation (SCSS) in hydrous silicate melts: With implications for arc magma genesis and sulfur recycling

Modeling the effect of H2O on the “sulfur content at sulfide saturation” (SCSS) in silicate melt is essential for the estimation of SCSS in both arc magmas and slab melts. Here we present a thermodynamic approach, in which, SCSS in hydrous silicate melt has been modeled as a combination of S dissolving as S2− and HS−/H2S, based on the sulfide capacity (CS2−) and the hydro-sulfide capacity (CHS), respectively. By adopting the thermodynamic framework of O’Neill and Mavrogenes (2002), S dissolution as HS−/H2S can be modeled in an analogous fashion to that for modeling S2− in anhydrous melt with the relation: lnHSSCSS=-ΔG°Fes-FeO/RT+lnCHS-lnaFeOmelt+lnaFeSsulfide. To obtain an expression for CHS, we compiled published experimental data on SCSS in hydrous silicate melts covering a PT range of 0.15–3 GPa and 785–1600 °C, and melt H2O contents of ∼1–13 wt%. While the contribution of S dissolving as S2− in basaltic and andesitic melts can be calculated based on the updated SCSS model for anhydrous basic melt from O’Neill (2021), S2− is considered negligible in rhyolitic and dacitic melts, i.e., when melt FeO content <∼5 wt%. We propose an expression for CHS as a function of temperature, mole fractions of cations for the normalized anhydrous melt composition, ln(XOH + XH2O), and a Na + K-Al term for alkaline-enriched rhyolitic melts. The coefficients for cation mole fractions are adopted from the expression for CS2− from O’Neill (2021); the coefficients for the 1/T and Na + K-Al terms are obtained from regression. The reproducibility of compiled SCSS values is ±50% for hydrous rhyolitic and dacitic melts, and ±10–30% for hydrous basaltic and andesitic melts, representing a significant improvement in comparison to previous models.Our model produces SCSS values for the primitive arc magmas compiled by Ruscitto et al. (2012), that are in most cases higher than the measured S contents, implying sulfide under-saturated conditions during mantle wedge melting. The contribution of H2S dissolution to the calculated SCSS values varies in a range of 70–1234 ppm, which increases with the increase of H2O content (0.3–6.2 wt%). H2S dissolution therefore contributes to the higher S content in arc basalt compared to MORB, an observation which is further corroborated by the positive correlation between H2O and S contents in primitive arc magmas. Applying our current model to experimentally produced sediment melts spanning a PT range of 690–1050 °C and 2.5–4.5 GPa, demonstrates that sediment melts, especially those of intermediate supercritical character with >25 wt% H2O and peralkaline in composition, can have high SCSS values as a result of H2S dissolution, and act as the transfer medium for S recycling between the slab and mantle wedge under reduced conditions.

Electrochemical behaviour of LiCl-KCl eutectic melts containing moisture as impurity. Part II: Uranium electrode

In Part I, LiCl-KCl eutectic melt purified by chlorine and LiCl-KCl + xwt.% H2O prepared by thermal equilibration of eutectic mixture with H2O at 500 °C were analysed for moisture content using acid-base titration. They were further investigated by electrochemical impedance spectroscopy (EIS) at inert tungsten electrode. It was established that cathodic reduction of H2O led to formation of OH- that adsorbed on tungsten electrode in potential range −0.80 to −1.50 V. The OH- film contributed to capacitive response as well as it offered a resistance to any other faradaic process occurring in that potential range. In this work, same LiCl-KCl eutectic melts were used to explore the anodic dissolution of uranium electrode in potential range −1.40 to −0.90 V by EIS. Complex impedance data in all melts were fitted to different equivalent circuit models. Presence of OH- film, which influenced the dissolution of uranium in LiCl-KCl + H2O melts, was modelled using additional resistor and constant phase elements in the equivalent circuit. Impedance data were further validated by Kramers-Kronig transforms where pseudo-χ2 values varied from 8.5×10−6 to 1.2×10−4 confirming a good compliance with spread of fit residuals across logω limited to less than ±3%. After EIS measurements, melts were again analysed by cyclic voltammetry and additional voltammetric features complicating the redox behaviour of U3+|U couple were analyzed.

VESIcal: 2. A Critical Approach to Volatile Solubility Modeling Using an Open‐Source Python3 Engine

AbstractAccurate models of H2O and CO2 solubility in silicate melts are vital for understanding volcanic plumbing systems. These models are used to estimate the depths of magma storage regions from melt inclusion volatile contents, investigate the role of volatile exsolution as a driver of volcanic eruptions, and track the degassing path followed by a magma ascending to the surface. However, despite the large increase in the number of experimental constraints over the last two decades, many recent studies still utilize an earlier generation of models which were calibrated on experimental datasets with restricted compositional ranges. This may be because many of the available tools for more recent models require large numbers of input parameters to be hand‐typed (e.g., temperature, concentrations of H2O, CO2, and 8–14 oxides), making them difficult to implement on large datasets. Here, we use a new open‐source Python3 tool, VESIcal, to critically evaluate the behaviors and sensitivities of different solubility models for a range of melt compositions. Using literature datasets of andesitic‐dacitic experimental products and melt inclusions as case studies, we illustrate the importance of evaluating the calibration dataset of each model. Finally, we highlight the limitations of particular data presentation methods, such as isobar diagrams, and provide suggestions for alternatives, and best practices regarding the presentation and archiving of data. This review will aid the selection of the most applicable solubility model for different melt compositions, and identifies areas where additional experimental constraints on volatile solubility are required.

Crystallization of peralkaline rhyolitic magmas: pre- and syn-eruptive conditions of the Pantelleria system

Pantelleritic magmas are low-viscosity peralkaline rhyolites which exhibit large differences in eruptive style (explosive to effusive). The processes that promote fragmentation and explosive eruptions of pantelleritic magma remain subject to debate, but undoubtedly variations of magma viscosity during magma ascent and degassing contribute to differences in eruptive style. Because crystallization can significantly influence magma rheology, we present a review of equilibrium and disequilibrium crystallization experiments of pantellerites, focusing on the crystallization of the main phases, alkali feldspar, and (lesser) clinopyroxene. Our analysis of data for several explosive pantelleritic eruptions on Pantelleria suggests pre-eruptive pressures of 50–100 MPa, temperatures of 700–800 °C for water-saturated conditions. Given these conditions, we show that the low pre-eruptive crystal fractions (0.08 to 0.15), temperatures between 700 and 800 °C, and the decrease of melt H2O content during magma ascent/decompression can promote a significant change in viscosity (up to 106–107 Pa·s), leading to magma brittle fragmentation and explosive eruptions. Because of their typical range of viscosity, pantelleritic magmas may show greater variations in eruptive style due to differences in ascent (decompression) rate when compared with metaluminous rhyolites.

Volcanological evolution of Montagne Pelée (Martinique): A textbook case of alternating Plinian and dome-forming eruptions

Montagne Pelée is one of the most active volcanoes of the Lesser Antilles arc, with two to three magmatic eruptions per millennium and an estimated magmatic production rate in the order of 0.7 km3/1000 years. Montagne Pelée is also infamous for the very large number of people (30000) killed by an eruptive phenomenon at the onset of the 1902–1905 dome-forming eruption. Active for ~550 kyrs, Montagne Pelée has undergone two major flank collapses that influenced its volcanological as well as magmatic evolution. The last one occurred at around 36 ka. Due to changes in the threshold effect following the decrease in load of the volcanic edifice due to flank collapse, there was a switch in emitted magma from generally andesitic to basaltic andesites. After 10 kyrs of intense activity, the load exerted by the new edifice once again prevented dense basaltic andesite magma from reaching the surface, whereas andesitic magmas, similar to the initial ones, continued to be emitted. All the magmas come from a common magma ponding zone at 200 ± 50 MPa, 875 ± 25 °C, an oxygen fugacity (fO2) between 0.4 and 0.8 log unit above the nickel‑nickel oxide (NNO) oxygen buffer, and melt H2O contents of 5.3–6.3 wt%. Based on comparative on-land and marine tephrochronological studies, we have reconstructed a detailed eruptive history of the volcano over the last 25 kyrs. The volcano produced a succession of Plinian-SubPlinian and dome-forming eruptions, making it a textbook case for studying this duality, which sometimes occurred during a single eruption. We identified more than 55 magmatic eruptions, with a ratio of 2/3 for dome-forming vs. Plinian eruptions. An unusual feature of this volcano is that dome-forming eruptions often start with violent, superficial and laterally directed explosions. These generate highly devastating dilute and turbulent pyroclastic density currents on the southwestern and southern flanks of the volcano, as illustrated by the seven events of this type during the first months of the 1902–1905 eruption. On the basis of the past eruptions over the last millennia, a series of scenarios can be proposed in the event of reactivation, including no magmatic eruption, a phreatic event or a magmatic eruption (Plinian or dome-forming eruption, with or without an explosive phase).

X-ray free electron laser heating of water and gold at high static pressure

Probing of reactive materials such as H2O ices and fluids at the high pressures and temperatures of planetary interiors is limited by unwanted chemical reactions and confinement failure. Faster experiments can mitigate such issues, but the common approach of adiabatic compression limits the conditions achieved. This study demonstrates a fast experimental strategy for the creation and probing of selected extreme states using static compression coupled with ultrafast X-ray laser heating. Indirect X-ray heating of H2O through the use of a gold absorber is evidenced by sample melting inferred from textural changes in the H2O diffraction lines and inter-dispersion of gold and H2O melts. Coupled with numerical analysis of femtosecond energy absorption, thermal equilibration, and heat transfer, all evidence indicates that temperatures in excess of an electron volt have been reached in the H2O at high pressure. Even after repeated heating, samples stayed chemically unchanged from the starting material.

Calbuco, a monotonous andesitic high-flux volcano in the Southern Andes, Chile

Calbuco (41.3°S) is a highly active composite frontal arc volcano in the Andean Central Southern Volcanic Zone (CSVZ). It is currently ranked by Chile's Geological Survey (SERNAGEOMIN) as among the most dangerous volcanic centers in the Southern Andes, with sub-Plinian explosive activity occurring as recently as 2015. Compositional and geochronologic data from 65 samples constrain the Pleistocene-Holocene eruptive evolution of Calbuco. New 40Ar/39Ar ages from lava flows, revised mapping, and existing 14C dates for Holocene tephras reveal that much of the current edifice is <20 ka in age. Thus, Calbuco has produced a greater Holocene eruptive flux, 3.4 km3/ka averaged over the last 10 ka and 4.8 km3/ka over the last 4 ka, than other arc volcanoes both in the CSVZ and globally. Morphologic and stratigraphic observations along with new whole-rock geochemical data suggest that this remarkable magma flux is expressed as repeated eruptions of lavas and tephra with a narrow SiO2 range (54–58 wt%). This compositional monotony, conspicuous resorbed amphibole, and elevated fluid-mobile trace element abundances differ from the post-glacial compositions and mineralogy observed at other CSVZ arc front volcanoes. Mid-crustal processing at or just below the depth where amphibole is stable plays a key role in the genesis of andesite at Calbuco. The precision of 40Ar/39Ar dates from Latest Pleistocene to Holocene low K2O mafic lavas remains a challenge to constructing eruptive chronologies for comparison to records of glacier expansion and retreat. Notwithstanding, our findings from Calbuco imply that petrologic factors, including mantle melt flux, depth of magma storage, and melt H2O content, may promote distinctive eruptive responses at adjacent CSVZ volcanoes following rapid retreat of the Patagonian Ice Sheet at 18 ka.

Crystallization and melt extraction of a garnet-bearing charnockite from South China: Constraints from petrography, geochemistry, mineral thermometry, and rhyolite-MELTS modeling

AbstractSince granitic rocks in high-grade terranes commonly undergo amphibolite-granulite facies meta-morphic overprint, recovering magmatic records from the metamorphic modification remains a major challenge. Here, we report an early Paleozoic, garnet-bearing Yunlu charnockite that outcropped in the Yunkai terrane of the Cathaysia block from South China and underwent amphibole-grade metamorphic overprint in the late Devonian. Field observation, micro-texture, and mineral geochemistry combined with diffusion modeling constrain that the metamorphic overprint with an extremely short duration of ~0.2–0.5 Ma only influences a narrow rim of &amp;lt;100 μm for most minerals. The magmatic information can be retrieved by combining rhyolite-MELTS modeling with mineral thermobarometry using mineral core compositions to quantitatively estimate magmatic pressure, temperature, and melt H2O contents. Rhyolite-MELTS modeling results are evaluated by comparison with experimentally determined phase relations for a peraluminous granite with ~69.83 wt% SiO2 at a pressure of ~500 MPa. The comparison suggests that the modeling reproduces phase relationships of feldspars and quartz within 20–60 °C when the melt H2O contents are below 7.0 wt%, but fails to account properly for all the phases when the melt H2O contents are higher than 7.0 wt%. The modeling results using reconstructed primary magma composition of the Yunlu charnockite combined with the orthopyroxene-garnet-plagioclase-quartz thermobarometry and fluid inclusion analyses suggest that the magma was emplaced at a pressure of ~600 MPa, a temperature of &amp;gt;900 °C, and an initial H2O content of ~4.0 wt% with rare CO2 components. The orthopyroxene-garnet, biotite-garnet, and biotite-orthopyroxene thermometers yield a consistent temperature range of 770–820 ± 60 °C, which is significantly higher than the H2O-saturated solidus temperature of ~630 °C estimated from experimental results and two-feldspar thermometry. These results indicate that the early crystallized minerals (e.g., garnet, orthopyroxene, and some euhedral biotite) of the Yunlu charnockite equilibrate at higher temperatures with crystallinities of ~30–45%, rather than the H2O-saturated solidus conditions. We thus propose a hypothesis of melt extraction at 780–820 °C in a deep-seated, slowly cooling, partially crystalline magma reservoir. The melt extraction physically segregates the early crystallized minerals from residual interstitial melts, which inhibits element diffusion equilibration between these minerals and interstitial melts. Granite thermometry commonly yields a large range of temperature estimations, which may be related to melt extraction events. Our study shows that melt extraction recorded in granites can be identified by combining micro-texture, mineral thermometry and rhyolite-MELTS modeling, which further provides quantitative insights into the fractionation process of silicic magmas.

Mineral and whole-rock chemistry of the Chating porphyry Cu--Au deposit related intrusions in the Middle-Lower Yangtze River Belt, Eastern China: Implications for magma evolution and mineralization

The Chating deposit is the largest Cu--Au porphyry deposit in the Xuancheng district of the Middle-Lower Yangtze River Metallogenic Belt. It is associated with three intrusive phases, an amphibole diorite porphyry, an ore-bearing quartz diorite porphyry and a late diorite porphyry. The amphibole diorite porphyry and quartz diorite porphyry are characterized by large ion lithophile element enrichment, depleted high field strength elements, low Yb/Lu and Y/Yb ratios, low εHf(t) (−8.29 to −12.02), εNd(t) (−6.93 to −7.42), and high 87Sr/86Sr(i) (0.705723 to 0.705802), suggesting a source comprised of both subduction-modified mantle- and crust-derived materials. The zircon U--Pb ages of the amphibole diorite porphyry (138.8 ± 3.0 Ma) and quartz diorite porphyry (137.6 ± 3.0 Ma) are consistent with their cross-cutting relationships and within error of the average molybdenite Re--Os age of 136.0 ± 1.3 Ma, suggesting that the Chating porphyry mineralization belongs to the early metallogenic event in the Middle-Lower Yangtze River Metallogenic Belt. Both the amphibole diorite porphyry and quartz diorite porphyry contain high and low Al amphiboles. The high Al amphiboles from the two intrusions show similar ranges of calculated temperatures (842 to 908 °C), pressures (143 to 229 MPa; corresponding to depths of 5.2 to 8.6 km), melt H2O contents (2 to 4 wt%), ΔNNO values (0.12 to 0.99), and Mg# (57 to 65), suggesting coeval crystallization in the same magma chamber. The low Al amphiboles with higher Mg# (68 to 75) formed at lower temperatures (711 to 812 °C) and pressures (49 to 89.3 MPa; corresponding depth of 1.9 to 3.4 km). The core-rim textures and abrupt compositional changes of amphibole and plagioclase from the amphibole diorite porphyry suggest that mafic magma was repeatedly injected into the magma chamber. In contrast, the patchy amphiboles and oscillatory zoned plagioclases in the quartz diorite porphyry may result from continuous fractional crystallization of biotite, amphibole, and plagioclase which would have increased the metal content and fO2 of the residual magma, and resulted in the exsolution of ore-forming fluids.

Apatite Crystals Reveal Melt Volatile Budgets and Magma Storage Depths at Merapi Volcano, Indonesia

Abstract Magma volatile budgets and storage depths play a key role in controlling the eruptive styles of volcanoes. Volatile concentrations in the melt can be inferred from analyses of glass inclusions, which however may not be present in the investigated rocks or may have experienced post-entrapment processes that modify their volatile records. Apatite is becoming an alternative robust tool for unraveling the information of magmatic volatiles. Here we report a comprehensive dataset for the concentrations of volatiles and major elements in apatite crystals in the rocks from two eruptions with contrasting eruptive styles: the 2006 (dome-forming) and 2010 (explosive) eruptive events at Merapi volcano (Java, Indonesia). We obtained two-dimensional compositional distributions and in situ concentrations of H2O, CO2, F, Cl and S in 50 apatite crystals occurring at various textural positions. The CO2 concentrations we report are probably the first ones from natural volcanic apatite. Using the volatile concentrations in apatite and existing thermodynamic models and geothermobarometers, we have calculated the volatile abundances of the pre-eruptive melts of the two eruptions. We find that the apatite from the 2006 and 2010 deposits have a similar compositional range of volatiles, with a bimodal distribution of F–H2O–CO2 contents. The apatite included in amphibole has higher H2O (0·9–1·0 wt %) and CO2 (≥2400 ppm), but lower F (0·9–1·4 wt %), compared to crystals included in plagioclase, clinopyroxene, or in the groundmass (H2O: 0·4–0·7 wt %; CO2: 40–900 ppm; F: 1·7–2·3 wt %). Using these volatile concentrations and apatite-melt exchange coefficients we obtained two distinct ranges of H2O–CO2–S–F–Cl concentrations in the melt. Melts in equilibrium with apatite included in amphibole had 3–8 wt % H2O, ≥8000 ppm CO2, 340–2000 ppm S, whereas melts in equilibrium with apatite included in anhydrous minerals and in the groundmass had lower H2O (1·5–4 wt %), CO2 (60–2500 ppm), and S (10–130 ppm). We calculated the melt H2O–CO2 saturation pressures and found that they correspond to two main magma storage depths. The shallow reservoir with melts stored at ≤10 km below the crater agrees with the depths constrained by melt inclusions, as well as the geodetic, geophysical and seismic tomography studies from the literature. We have also found a significantly deeper melt storage zone at ≥25–30 km recorded by the C- and H2O-rich apatite in amphibole and barometry calculations using amphibole and high-Al clinopyroxene, which matches with the depths reported in seismic tomography studies. The high CO2/H2O and CO2/SO2 concentrations of the deep melt can help to explain the sharp increase in these ratios in fumarolic gas that were sampled just before the eruption in 2010. Supply of deep volatiles to the shallower magma column before the eruption in 2010 could have increased the magma buoyancy, and thus led to higher magma ascent rates and associated eruption explosivity. Evidence for the faster pre-eruptive magma ascent in 2010 than 2006 is also found on the diffusion distance of Cl in apatite microlites.

Effects of sulfide composition and melt H2O on sulfur content at sulfide saturation in basaltic melts

Sulfur content at sulfide saturation (SCSS) is a critical parameter that controls the consumption of sulfide during partial melting as well as potential exsolution of sulfide during magma evolution. Natural magmatic systems involve H2O in silicate melt and NiS in FeS-dominated sulfide, but the combined effects of melt H2O and sulfide composition on SCSS have not been well constrained. We carried out 18 phase equilibrium experiments between anhydrous or hydrous basaltic melt and FeS-NiS sulfide at 1.0–2.5 GPa and 1523–1673 K in a piston cylinder apparatus. Experimental results demonstrate an increase of SCSS of approximately 104 ppm per wt% melt H2O and a proportional increase of SCSS with the mole fraction of FeS in sulfide (XFeS). In combination with literature data, we find that the effects of melt H2O and sulfide composition are independent and additive. A new model of SCSS for natural basaltic melt is developed:SCSS(ppm)=XFeS⋅exp13.88−9744T−328PT+104wH2O,where T is temperature in K, P is pressure in GPa, and wH2O is melt H2O content in wt%. This model not only fits our own data well but also reproduces literature data of SCSS in basaltic melt within 20% off. Application of this SCSS model to ridge magmatism shows that the observed S contents in MORBs corresponds to ~15% melting of mantle (after sulfide exhaustion). The higher S contents in some sulfide-saturated MORBs require a mantle source containing high-NiS sulfide (XNiS ≈ 0.4). Comparison of SCSS with S contents in melt inclusions from primary arc magmas suggests that sulfate is not required to be present for a majority of sub-arc mantle.

Constraints on deep, CO2-rich degassing at arc volcanoes from solubility experiments on hydrous basaltic andesite of Pavlof Volcano, Alaska Peninsula, at 300 to 1200 MPa

Abstract The solubility of CO2 in hydrous basaltic andesite was examined in fO2-controlled experiments at a temperature of 1125 °C and pressures between 310–1200 MPa. Concentrations of dissolved H2O and CO2 in experimental glasses were determined by ion microprobe calibrated on a subset of run glasses analyzed by high-temperature vacuum manometry. Assuming that the solubility of H2O in mafic melt is relatively well known, estimates of XH2Ofluid and PH2Ofluid in the saturating fluid were modeled, and by difference, values for XCO2fluid and PCO2fluid were obtained (XCO2 ~0.5–0.9); fCO2 could be then calculated from the fluid composition, temperature, and pressure. Dissolved H2O over a range of 2.3–5.5 wt% had no unequivocal influence on the dissolution of CO2 at the pressures and fluid compositions examined. For these H2O concentrations, dissolved CO2 increases with fCO2 following an empirical power-law relation: dissolved CO2 (ppmw) = 14.9−3.5+4.5[fCO2 (MPa)]0.7±0.03. The highest-pressure results plot farthest from this equation but are within its 1 standard-error uncertainty envelope. We compare our experimental data with three recent CO2-H2O solubility models: Papale et al. (2006); Iacono-Marziano et al. (2012); and Ghiorso and Gualda (2015). The Papale et al. (2006) and Iacono-Marizano et al. (2012) models give similar results, both over-predicting the solubility of CO2 in a melt of the Pavlof basaltic andesite composition across the fCO2 range, whereas the Ghiorso and Gualda (2015) model under-predicts CO2 solubility. All three solubility models would indicate a strong enhancement of CO2 solubility with increasing dissolved H2O not apparent in our results. We also examine our results in the context of previous high-pressure CO2 solubility experiments on basaltic melts. Dissolved CO2 correlates positively with mole fraction (Na+K+Ca)/Al across a compositional spectrum of trachybasalt-alkali basalt-tholeiite-icelandite-basaltic andesite. Shortcomings of current solubility models for a widespread arc magma type indicate that our understanding of degassing in the deep crust and uppermost mantle remains semi-quantitative. Experimental studies systematically varying concentrations of melt components (Mg, Ca, Na, K, Al, Si) may be necessary to identify solubility reactions, quantify their equilibrium constants, and thereby build an accurate and generally applicable solubility model.