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In a deforming partially molten rock, melt concentrates into a grain‐scale melt pocket aligned at a preferred orientation (melt‐preferred orientation, or MPO). However, observing this texture alone provides limited information on the 3D orientation and geometry of these melt pockets, which are critical parameters for estimating permeability. Here, we modeled the MPO of experimentally deformed peridotites by simulating melt streaks arising from melt pockets of various shapes and 3D orientations. The model aims to identify 3D distribution and characteristics of melt pockets that could account for the observed length, thickness, and the probability of melt streaks. Results show that melt pockets at preferred orientation exhibit greater length, thickness, and number density compared to those perpendicular. These results can be incorporated into the simulation of melt flow through individual melt pockets, which allows us to estimate the permeability corresponding to the observed MPO. We found that the permeability of vertically compressed peridotites increases with increasing compressive strain and a more elongated and thickened shape for melt pocket aligned at preferred orientation. The vertical permeability in the sample with 30% compressive strain is at least 40 times larger than that of an undeformed sample. For peridotites deformed under simple shear, the permeability exhibits an anisotropy of at least three. Such anisotropic permeability, coupled with the formation of melt‐rich bands and other melt channels, is believed to cause lateral melt focusing beneath mid‐ocean ridges. Plain Language Summary The distribution of melt at the grain scale controls the permeability in partially molten rock. While observe melt streaks on thin sections show variations in length and thickness with respect to the orientation, the geometry and distribution of melt pockets in 3D are poorly constrained. Here, we use an improved statistical model to identify the dependence of melt pocket dimensions as functions of orientation. We further calculate melt flux through individual melt streaks and estimate permeability corresponding to the observed melt distribution texture. We found that deformation in the mantle can significantly accelerate melt extraction and potentially bend the melt flow using anisotropic permeability. Key Points We parameterized the 3D shapes and orientations of melt pockets under the constraints of observed melt‐preferred orientation (MPO) Permeability in peridotites deformed under vertical compression increases with compressive strain and demonstrates anisotropy up to two Permeability in peridotites deformed under simple shear demonstrates anisotropy of at least three

Repacking enhances crystal mush permeability, accelerating melt extraction. However, identifying microstructural records of repacking is challenging, creating a gap in quantifying its effect on magmatic reservoirs. We identified extracted melt (rhyolite) and silicic residue (quartz monzonite) through textures and geochemical characteristics in the Pangduo Basin (Southern Tibet; ∼50 Ma old). By calculating interstitial mineral proportions and modeling incompatible element concentrations in quartz monzonite, we estimate a moderate trapped melt fraction (∼50 vol. %), providing microtextural evidence of repacking at intermediate crystallinities. We interpret that the horizontal preferred orientation of frame‐forming feldspars produces micro‐scale melt channels that accelerate melt extraction. Modeling the intensity of this orientation, we estimated compressive strain to be 20%–30%, likely accelerating melt extraction by at least 15 times. This millennium timescale allows for the growth of a large magma chamber, preventing the melt from freezing or causing multiple small eruptions due to excessive flow‐induced stress. Plain Language Summary Explosive rhyolite eruptions significantly affect climate, the environment, and human life. These devastating events, involving crystal‐melt separation in large upper crustal magma reservoirs, may be accelerated by grain reorganization. Yet, quantifying this acceleration is complex. Our study utilizes samples from the Pangduo Basin in southern Tibet to examine the pertinent microstructure and calculate the acceleration rate of crystal‐melt separation. We found that grain reorganization can reduce the separation duration by a factor of 15, highlighting its critical role in crystal‐melt separation. Key Points The rhyolite and quartz monzonite of the Pangduo Basin represent extracted melt and corresponding residual cumulates, respectively Interstitial minerals fraction and mass‐balance calculations yield a moderate trapped melt fraction of ∼50 vol. % The horizontal preferred orientation of large‐grained feldspars accelerates melt extraction by at least 15 times

The structure and evolution of the magma plumbing system that produced the dacitic Yukiura Pumice (YP) at Iwate volcano, northern Honshu, are constrained by petrography and rhyolite–MELTS simulations. The basaltic Yukiura Scoria (YS) eruption immediately preceded YP, marking a bimodal shift in erupted compositions. For YS, whole-rock MELTS runs that reproduce the observed phenocryst assemblage support hydrous basalt (3–4.25 wt% H 2 O). Plagioclase (An 86–92 ) crystallized during 200–70 MPa decompression/cooling, followed by olivine (Fo 73–75 ) at 90–40 MPa. Plagioclase in YP dacite shows clear, normally zoned, patchy, and oscillatory textures. Correlating domains yields a thermal history: An fell from ~ 90 to ~ 60 with cooling, rose to 65–80 during a resorption event, then declined again; later, local fluctuations persisted within An 45–60 (mostly 50–55). Whole-rock MELTS calculations for YP match modal mineralogy and crystallinity but underpredict plagioclase An, demonstrating disequilibrium between crystals and bulk magma. Accordingly, most plagioclase—and cotectic mafic phases—are interpreted as antecrysts derived from less evolved magma. To reconcile petrography and chemistry, we model MECE (melt extraction with crystal entrainment): residual liquid is extracted from a high-crystallinity mafic mush while entraining crystals as antecrysts. Using groundmass as melt and observed phenocrysts as crystal phases, MELTS runs on a 90% crystalline, high-Fe/Mg basaltic mush (H 2 O > 3.5 wt%) at 350 MPa reproduce the observed phase relations, mineral chemistry, groundmass composition, and REE patterns. The preferred thermal path involves cooling from liquidus to 815 °C, episodic reheating and dehydration near the solidus, and final warming to 880 °C immediately before eruption. We infer that before the YS–YP sequence, basalt ascending beneath East Iwate intruded laterally at shallow depth and built a crystal mush that became the YP source. Injection of YS-type magma reheated this mush and triggered the extraction and eruption of the YP dacite. Graphical Abstract

With the aim to better understand the cause of the iron isotope heterogeneity of mantle-derived bulk peridotites, we compared the petrological, geochemical and iron isotope composition of four xenolith suites from different geodynamic settings; sub-arc mantle (Patagonia); subcontinental lithospheric mantle (Cameroon), oceanic mantle (Kerguelen) and cratonic mantle (South Africa). Although correlations were not easy to obtain and remain scattered because these rocks record successive geological events, those found between δ 57 Fe, Mg#, some major and trace element contents of rocks and minerals highlight the processes responsible for the Fe isotope heterogeneity. While partial melting processes only account for moderate Fe isotope variations in the mantle (<0.2 ‰, with bulk rock values yielding a range of δ 57 Fe ± 0.1 ‰ relative to IRMM-14), the main cause of Fe isotope heterogeneity is metasomatism (>0.9 ‰). The kinetic nature of rapid metasomatic exchanges between low viscosity melts/fluids and their wall-rocks peridotite in the mantle is the likely explanation for this large range. There are a variety of responses of Fe isotope signatures depending on the nature of the metasomatic processes, allowing for a more detailed study of metasomatism in the mantle with Fe isotopes. The current database on the iron isotope composition of peridotite xenoliths and mafic eruptive rocks highlights that most basalts have their main source deeper than the lithospheric mantle. Finally, it is concluded that due to a complex geological history, Fe isotope compositions of mantle xenoliths are too scattered to define a mean isotopic composition with enough accuracy to assess whether the bulk silicate Earth has a mean δ 57 Fe that is chondritic, or if it is ~0.1 ‰ above chondrites as initially proposed.

The separation of melt from crystals is a fundamental process driving the chemical differentiation of magmas and can lead to the formation of pockets of potentially eruptible magmas in highly crystallised magma reservoirs. While geochemical and geophysical evidence exists for the presence of such isolated pockets of eruptible melt, the processes that control their volume and spatial arrangement remain unclear. The Muroto sill in Japan provides an excellent opportunity to study these processes as it is perfectly exposed and shows clear evidence for melt segregation. We collected geochemical and structural data across the sill and performed thermal modelling to quantify extraction timescales and to constrain the range of crystallinity at which melt extraction occurred. Our data and calculations show that the middle–lower portion of the sill experienced melt extraction at crystal fractions between 0.65 and 0.8 over 100–150 years, until magma was too crystalline for further segregation to occur. We propose a new approach that can be used to invert measured geochemical profiles and identify the range of crystallinity at which melt extraction takes place. With this approach, the results we obtain for the Muroto sill can be generalised to magma reservoirs of different sizes and chemistries. Our calculations, and the comparison with natural magmatic systems, show that the volume of melt-rich pockets in a magma reservoir is proportional to the reservoir volume, while their spatial arrangement depends on the physiochemical properties of magmas. The results of this study increase our understanding of the factors controlling the distribution and volume of pockets of eruptible magmas in large magma reservoirs. Our calculations show that eruptible magma in dacitic and rhyolitic magma reservoirs, which are responsible for some of the largest eruptions on Earth, tend to be distributed in lenses of small volume within highly crystallised magma. Such architecture diminishes our capacity of identifying eruptible magma in large magma reservoirs such as Yellowstone using geophysical methods, and jeopardises our capacity of assessing the potential of a reservoir to feed a large eruption.

The highly regarded Fe2P-based magnetocaloric materials are usually fabricated by ball milling, and require an additional extended annealing treatment at high temperatures (at temperatures up to 1423 K for several hours to days). In this work, we show that fabricating Mn1.3Fe0.6P0.5Si0.5 into the form of microwires attained 82.1 wt.% of the desired Fe2P phase in the as-cast state. The microwires show a variable solidification structure along the radial direction; close to the copper wheel contact, Fe2P phase is in fine grains, followed by dendritic Fe2P grains and finally secondary (Mn,Fe)5Si3 phase in addition to the dendritic Fe2P grains. The as-cast microwires undergo a ferro- to para-magnetic transition with a Curie temperature of 138 K, showing a maximum isothermal magnetic entropy change of 4.6 J kg−1 K−1 for a magnetic field change of 5 T. With further annealing, a two-fold increase in the maximum isothermal magnetic entropy change is found in the annealed microwires, which reveal 88.1 wt.% of Fe2P phase.

In order to achieve process intensification for adsorption chillers and heat pumps, a new composite material was developed based on sintered aluminum fibers from a melt-extraction process and a dense layer of silico-aluminophosphate (SAPO-34) on the fiber surfaces. The SAPO-34 layer was obtained through a partial support transformation (PST) process. Preparation of a composite sample is described and its characteristic pore size distribution and heat conductivity are presented. Water adsorption data obtained under conditions of a large pressure jump are given. In the next step, preparation of the composite was scaled up to larger samples which were fixed on a small adsorption heat exchanger. Adsorption measurements on this heat exchanger element that confirm the achieved process intensification are presented. The specific cooling power for the adsorption step per volume of composite is found to exceed 500 kW/m3 under specified conditions.

Spent nuclear fuel, in Sweden, is planned to be put in 50-mm thick copper canisters and placed in 500-m depth in the bedrock. Depending on the conditions in the repository, an uptake of hydrogen in the copper may occur. It is therefore necessary to establish how a hydrogen uptake affects the microstructure in both the surface and the bulk. Phosphorus-doped, oxygen-free copper has been cathodically charged with hydrogen for up to 3 weeks. The amount of hydrogen as a function of the distance from the surface was measured by two methods: glow discharge optical emission spectrometry and melt extraction. The penetration of the increased hydrogen content was about 50 μm. Extensive bubble formation took place during the charging. A model has been formulated for the diffusion of hydrogen into the copper, the bubble formation and growth. The model can describe the total amount of hydrogen, the number of bubbles and their sizes as a function of the distance from the surface. Bubbles close to the surface caused the surface to bulge due to the high hydrogen pressure. From the shape of the deformed surface, the maximum hydrogen pressure could be estimated with the help of stress analysis. The maximum pressure was found to be about 400 MPa, which is almost an order of magnitude larger than previously recorded values for electroless deposited copper.

Ultra-thin (of a thickness of 10 nm) gold films have been deposited on the surface of different supports by electron-beam deposition. The supports comprised titanium and zirconium fibers formed by the pendant drop melt extraction and titanium plates treated by plasma electrolytic oxidation. The Au/Zr, Au/Ti (based on fibers), and Au/TiO 2 /Ti (based on oxidized titanium) composites have been tested in the CO oxidation reaction. It has been shown that the deposition of gold increases the catalytic activity of titanium and zirconium fibers, but has an insignificant effect on the activity of oxidized titanium. It was established that, upon contact with a gas mixture at temperatures up to 500°C, gold particles were accumulated in droplets, the size and number of which depended on the nature of the metal and the thickness of the oxide film on its surface.

In the Central American Volcanic Arc, adakite-like volcanism has often been described as volumetrically insignificant. However, extensive silicic adakitic volcanism does occur in the Panamanian arc and provides an opportunity to evaluate the origin of this magma-type as well as to contrast its origin with other Central American silicic magmas. The Quaternary volcanic deposits of El Valle volcano are characterized by pronounced depletions in the heavy rare earth elements, low Y, high Sr, high Sr/Y, relatively high MgO, and low K 2 O/Na 2 O, when compared with other Quaternary Central American volcanics at similar SiO 2 . These chemical features are also diagnostic of adakitic signatures. Our new 40 Ar/ 39 Ar ages of lava flows and ash flows that compose the volcanic edifice of El Valle volcano illustrate that the eruptive volume of adakitic-like volcanism is substantial during the Quaternary (~120 km 3 ). Adakitic-like magmas dominate the stratigraphic record. Common to all models for the origin of an adakite geochemical signature is the involvement of garnet, as a residual or fractionating phase. The stability of garnet in hydrous magmas has been recently reevaluated with important consequences; garnet is a stable primary igneous phase at pressure and temperature conditions expected for magma differentiation at the roots of a mature island arc. Moreover, adakite-like volcanism erupted at El Valle volcano displays the middle rare earth element depletion observed in other Panamanian volcanic centers that has been attributed to significant amphibole fractionation. Extensive amphibole fractionation may have occurred in two stages. The first stage of fractionation, garnet + amphibole fractionation, occurs from hydrous basaltic–andesitic parental magmas that have ponded at the base of an overthickened crust. The second stage occurs at mid-lower crustal levels where abundant amphibole + plagioclase and minor sphene crystallized from water-rich magmas. These two stages combined may have resulted in an amphibole-rich cumulate layer. This amphibole layer is likely the source of the abundant amphibole-rich cumulate enclaves and blobs found in volcanic products across the Panamanian arc. Stalling of water-rich magmas during this two-stage fractionation process could drive the interstitial liquids to the evolved compositions typical of continental crust, while leaving behind amphibole-rich cumulate rocks that may eventually be returned to the asthenosphere. Differentiation of H 2 O-rich magmas under the conditions appropriate for the roots of island arcs may therefore be a key process in developing a better understanding of the generation of continental crust in island arc environments.