Melting Region Research Articles

Why Are Plume Excess Temperatures Much Less Than the Temperature Drop Across the Lowermost‐Mantle Thermal Boundary Layer?

AbstractWhile temperature drop across the mantle's basal thermal boundary layer (TBL) is likely 1,000 K, the temperature anomaly of plumes believed to rise from that TBL is only up to a few hundred Kelvins. Reasons for that discrepancy are still poorly understood and a number of causes have been proposed. Here, we use the ASPECT software to model plumes from the lowermost mantle and study their excess temperatures. We use a mantle viscosity that depends on temperature and depth with a strong viscosity increase from below the lithosphere toward the lower mantle, reaching about Pas above the basal TBL, consistent with geoid modeling and slow motion of mantle plumes. With a mineral physics‐derived pyrolite material model, the difference between a plume adiabat and an ambient mantle adiabat just below the lithosphere is about two thirds of that at the base of the mantle, for example, 1,280 versus 835 K. 3D models of isolated plumes become nearly steady‐state 10–20 Myr after the plume head has reached the surface, with excess temperature drop compared to an adiabat for material directly from the core‐mantle boundary (CMB) usually less than 100 K. In the Earth, plumes are likely triggered by slabs and probably rise preferably above the margins of chemically distinct piles. This could lead to reduced excess temperatures, if plumes are more sheet‐like, similar to 2D models, or temperature at their source depth is less than at the CMB. Excess temperatures are further reduced when averaged over the plume conduit or melting region.

Characterization of in situ damage to tungsten PFCs induced by transient heat flux during plasma disruption in EAST

Abstract Transient heat flux of up to several thousand MW m−2 in a short pulse (∼ms) in tokamaks poses great risk to plasma-facing components (PFCs), making it a major concern for ITER. Despite numerous high heat flux tests, analysis of in situ transient heat flux-induced damage to PFCs remains necessary. Such damage, including the melting and cracking of tungsten (W) PFCs, is notably observed on the divertor (dome and baffle plates) and limiter in EAST. The damage is identified as being induced by runaway electron loss during plasma disruption at the beginning of each plasma campaign. It typically occurs at the leading edges or protruding parts of PFCs, sometimes accompanied by visible macrocracks. In terms of melting phenomena, three distinct grain layers can be observed from the molten surface to deeper regions, namely columnar grain, equiaxed grain (recrystallization region) and original grain. This grain distribution indicates a steep temperature gradient from the surface to the deeper regions during melting events, a characteristic feature for W under fusion-relevant transient heat flux loading. The surface morphologies of all melted PFCs are generally similar, characterized by undulated melting waves. The motion of the melting layer is primarily along the toroidal direction, as shown in the in situ melting of PFCs. The influence of the J × B force might not be significant due to the limited lifetime of the melting pool, which results in limited acceleration times and expected bulk melt displacement. The directions of plasma pressure and Marangoni flow, both along the toroidal direction, might be the dominant forces here. Additionally, cracks at the leading edges were observed on the divertor dome and baffle plates during post-mortem inspection. In some cases, dense cracks were visible in the melting region and even in areas far from the melting zone. It should be noted that cracks were only found in partially melted PFCs, which could be related to the base temperature when PFCs were hit by the runaway electron-induced transient heat flux. Furthermore, some columnar grains were observed to exfoliate from the material, indicating severe cracking. Since EAST has similar W PFCs to ITER, the transient heat flux-induced melting and cracking damage to W PFCs by runaway electrons during plasma disruption in EAST provide important references for ITER.

Seismic imaging of the Ecuadorian forearc and arc from joint ambient noise, local, and teleseismic tomography: catching the Nazca slab in the act of flattening

SUMMARY The Ecuadorian Andes are a complex region characterized by accreted oceanic terranes driven by the ongoing subduction of the oceanic Nazca plate beneath South America. Present-day tectonics in Ecuador are linked to the downgoing plate geometry featuring the subduction of the aseismic, oceanic Carnegie Ridge, which is currently entering the trench. Using seismic tomography, we jointly invert arrival times of P and S waves from local and teleseismic earthquakes with surface wave dispersion curves to image the structure of the forearc and magmatic arc of the Ecuadorian Andes. Our data set includes > 100 000 traveltimes recorded at 294 stations across Ecuador. Our images show the basement of the central forearc is composed of accreted oceanic terranes with high elastic wave speeds. Inboard of the Carnegie Ridge, the westernmost forearc and coastal cordilleras display relatively low Vp and Vs and high Vp/Vs values, which we attribute to the increased hydration and fracturing of the overriding plate due to the subduction of the thick oceanic crust of the Carnegie Ridge. We additionally image across-arc differences in magmatic architecture. The frontal volcanic arc overlies accreted terranes and is characterized by low velocities and high Vp/Vs indicative of partial melt reservoirs which are limited to the upper crust. In contrast, the main arc displays regions of partial melt across a wider range of depths. The Subandean zone of Ecuador has two active volcanoes built on continental crust suggesting the arc is expanding eastwards. The mid to lower crust does not show indications of being modified from the magmatic process. We infer that the slab is in the process of flattening as a consequence of early-stage subduction of the buoyant Carnegie Ridge.

Improving Air Conditioning Performance With Circular Phase Change Materials Based Heat Storage

ABSTRACTThis study analyzes the impact of using single and multiple circular phase change materials (PCMs) to enhance the performance of an air‐conditioning (AC) unit. The technique involves attaching a heat exchanger containing cold energy storage PCM to the air conditioner's condenser. During the daytime, warm surrounding air is cooled and transmitted to the condenser of the air‐conditioning system. The computational study is conducted using the SST k –ω turbulence model. The air inlet temperature to the PCM is kept at 308.15 K, and the air flow rate is kept constant at 49 L/s. The findings indicate that, during the discharging process, the complete melting time for the multi‐circular PCM increases by almost 72% compared to the single‐circular PCM. Temperature contours reveal that turbulence happens in the solid zone, primarily at higher temperatures, within the PCM melting region. This suggests enhanced convection in this region. The fall in the outlet air temperature is greater for the multi‐circular PCM relative to the single‐circular PCM. The coefficient of performance (COP) increases by approximately 87.57% for the multi‐circular PCM system and 7.60% for the single‐circular PCM unit during summer. The power saved by the single‐circular PCM is about 0.3792 W for 6 h of operation, while the multi‐circular PCM saves approximately 4.3821 W.

Research on the microwave heating and de-icing performance of various composite coatings

Abstract Microwave heating and de-icing is an efficient, eco-friendly choice for wind turbine blade de-icing methods, where microwave energy is converted into heat through absorbing coatings. Thus, the heating characteristics of absorbing coatings under microwave irradiation are of paramount importance. In this paper, 15 types of polyurethane composite coatings containing different absorbing fillers were prepared, and their heating performance under 2.45 GHz microwave irradiation was investigated. The effects of filler type, filler content and irradiation distance on heating rate were systematically evaluated, and the de-icing performance of various ice layer thicknesses was analyzed. Results revealed that ferroferric oxide/polyurethane coatings with an identical filler content exhibited the fastest heating rate, followed by graphite/polyurethane and silicon carbide/polyurethane. The heating characteristics of the coatings were positively correlated with filler content and negatively correlated with irradiation distance. As ice thickness increased, so did the time for ice shedding and melting. Composite coatings demonstrated superior de-icing performance compared with control specimens, creating a central melting region that gradually expanded to melt the entire ice layer.

CRUSTAL CARBONATITES: DEFINITION, GEOLOGY, MINERALOGY, AND GEOCHEMISTRY

This is a synopsis of the available data on crustal carbonatites, including their temporal and spatial distribution, mineralogy, geochemistry, and stable isotope (δ18O and δ13C) patterns. Crustal carbonatites are intrusive rocks containing >50 vol. % carbonate minerals and ≤20 wt. % SiO2, which crystallize from partial melts of primary sedimentary carbonate rocks in the lower crust. They commonly occur as dykes in high-grade metamorphic complexes, bear silicate minerals typical of metasomatic environments, show isotopic and geochemical signatures of carbonate sediments or transitional varieties to mantle-derived carbonatites, and are emplaced during tectonic activity in strike-slip, rifting, or postcollisional extension settings. Partial melting of carbonate material in the crust and intrusion of melt batches to shallower crust levels is possible provided that primary carbonate sediments are present in the lower crust while the melting region is heated up by underplated mantle mafic magma and is fluxed sufficiently with H2O-rich fluids.

Origin and Evolution of the Holocene Magmatic System at Sakurajima Volcano, Japan

Abstract Sakurajima volcano has developed since 26 ka through post-caldera magmatic activity at the Aira caldera (formed at 30 ka) and is one of the most active volcanoes in Japan. In this study, new petrological and geochemical analyses were conducted on proximal volcanic products to understand the origin and evolution of the magmatic system during the Holocene. The volcanic products have andesitic and dacitic compositions (58–69 wt % SiO2), and relatively older products (9–1.6 ka) and younger products (<1.3 ka) are characterised by having lower and higher P2O5 contents, respectively (low- and high-P2O5 groups, respectively). The low-P2O5 group products had lower TiO2 and Y contents, higher 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios, and lower 143Nd/144Nd ratios than the high-P2O5 group products. It is suggested that the low-P2O5 group magmas were produced by the partial melting of lower crustal materials, and the compositional variations primarily reflected the variation in the degree of melting, with some contribution from mixing with mafic magmas. In contrast, the high-P2O5 group magmas were produced by mixing mafic and felsic magmas in varying proportions. The mafic end-member magmas evolved from mantle-derived primitive magmas with some contribution from crustal assimilation. The felsic end-member magmas were produced by fractional crystallisation following the melting of lower crustal materials with higher melting degrees than those of the low-P2O5 group magmas. In summary, the geochemical evolution of Holocene magmatic activity at Sakurajima was essentially controlled by intermittent discharges of partial melts from the lower crustal source region with increasing melting degrees. The remnants of the voluminous Aira rhyolitic magmas from caldera-forming eruptions were not involved in the Holocene magmatic system. Lower crustal source materials that produced the Aira rhyolites were also not involved. The lower crustal melting region, which was the main source of Holocene magmatism at Sakurajima, may have already existed at ~100 ka, well before the caldera-forming eruption at 30 ka.

The progression of basaltic-rhyolitic melt storage at Yellowstone Caldera.

Yellowstone Caldera is one of the largest volcanic systems on Earth, hosting three major caldera-forming eruptions in the past two million years, interspersed with periods of less explosive, smaller-volume eruptions1. Caldera-forming eruptions at Yellowstone are sourced by rhyolitic melts stored within the mid- to upper crust. Seismic tomography studies have suggested that a broad region of rhyolitic melt extends beneath Yellowstone Caldera, with an estimated melt volume that is one to four times greater than the eruptive volume of the largest past caldera-forming eruption, and an estimated melt fraction of 6-28 per cent2-5. Seismic velocity is strongly influenced by temperature, pressure and melt; however, magnetotelluric data are primarily sensitive to the presence of melt, making these data ideal for constraining volcanic systems. Here we utilize magnetotelluric data to model the resistivity structure of Yellowstone Caldera's crustal magma reservoir and constrain the region's potential for producing major volcanic eruptions. We find that rhyolitic melts are stored in segregated regions beneath the caldera with low melt fractions, indicating that the reservoirs are not eruptible. Typically, these regions have melt volumes equivalent to small-volume post-caldera Yellowstone eruptions. The largest region of rhyolitic melt storage, concentrated beneath northeast Yellowstone Caldera, has a storage volume similar to the eruptive volume of Yellowstone's smallest caldera-forming eruption. We identify regions of basalt migrating from the lower crust, merging with and supplying heat to the northeast region of rhyolitic melt storage. On the basis of our analysis, we suggest that the locus of future rhyolitic volcanism has shifted to northeast Yellowstone Caldera.

Shock Compression of Coesite up to 950 GPa

AbstractExperimental investigations of silica under high pressure and temperature offer crucial insights into modeling of Earth and super‐Earths’ interiors. Despite extensive studies on Hugoniots of silica polymorphs like fused‐silica (2.20 g/cm3), quartz (2.65 g/cm3) and stishovite (4.29 g/cm3) up to a terapascal, unexplored region of melting and liquid of silica at high pressures is leaved because of the Hugoniots dependence on ambient density. This emphasizes the urgence to supplement the phase diagram to constrain silica properties under extreme conditions. Here, the Hugoniot and shock temperature of coesite (2.92 g/cm3) were studied by laser shock compression experiments up to 950 GPa. Our findings confirm shock‐induced superheating in coesite, revealing a higher Grüneisen parameter and lower electrical conductivity compared to those of fused‐silica and quartz along an isothermal line (<2 × 104 K). These results suggest unique properties of shocked coesite, which imply a warmer and longer‐lived silica magma ocean of earlier rocky‐planets.

Rudny Altai VMS-polymetallic belt (Russia, Kazakhstan) and its formation factors

The paper presents a modern metallogenic overview of Rudny Altai and the results of the study of the volcanic rocks associated with contrasting basalt-rhyolite formation, manifested as a consequence of riftogenic processes. There are two linear metallogenic subzones within the Rudny Altai polymetallic belt that extend in a northwestern direction. The Zmeinogorsko-Zyryanovskaya subzone is the main one: it contains 2/3 of the belt's deposits, 3/4 of Zn, Pb, Cu, and 4/5 of Au and Ag, which are associated with Emsian-Givetian basalt-rhyolite formation. The Irtysh metallogenic subzons extends along the Irtysh Shear Zone, and is mainly composed of the Eifelian – Early Famennian basalt-rhyolite formation. Devonian bimodal volcanism occurred against a background of extension deformation with the formation of pull-apart basins. Taking into account the structure-kinematic characteristics of faults, the Devonian architecture of the Rudny Altai block can be considered as a 'negative flower' (tulip) structures. Based on the trace element characteristics of initial basic rocks, the original magmas were the product of partial melting of metasomatised lithospheric mantle. This is confirmed by Pb-Pb studies of galena monofractions from the Rudny-Altai volcanogenic massive sulfide (VMS-type) deposits. The magma source of the subsequent major phases probably corresponded to the asthenosphere, which may have risen to the depth of the preceding melting region. The generation of significant volumes of felsic volcanic series, to which the main VMS-type deposits are genetically related, was most likely associated with large-scale melting of thick terrigenous strata of the pre-Devonian palaeoshelf under the influence of mantle magmas. The sequence of Devonian mineralization types is considered to be a consequence of the change in the type of volcanism initiated by transtension tectonics. This is consistent with the concept that the formation of ore-forming systems VMS type is associated with periods of hydrothermal activity during the mantle upwelling under extensive tectonic settings. For this region, the antidromic nature of magmatic series caused a specific evolution trend of its metallogeny, expressed in the change of barite-polymetallic and polymetallic deposits of the Emsian-Eifelian stage (Zyryanovskoe, Tishinka, Ridder-Sokolnoe), pyrite-polymetallic at the Givetian stage (Belousovskoe, Talovskoe) and then copper-pyritic at the Frasnian-Early Famennian stage (Kamyshinskoe, Nikolaevskoe). The results obtained are consistent with the model of evolution of the marginal arc – back arc system, in which mantle uplift is associated with basin extension and plate rollback.

Petrogenesis of granitoids from silicic large igneous provinces (Central and North-East Asia)

Large granitoid provinces can be divided into areal and linear types, which differ significantly in the area and volume of granitoids in their composition. It is shown using the example of the largest granitoid provinces of Central and Northeast Asia (Angara-Vitim, Khangai, Kalba-Narym, Kolyma). It is assumed that these differences are due to the structure of pregranitic basement and degree of thermal impact on the lower and middle continental crust. An important factor in the formation of granitoid provinces is mantle mafic magmatism, the estimated scale of which correlates with the volumetric and areal characteristics of the granitoid provinces. The role of mafic magmatism is an additional input of heat from the fluids into the melting region of crustal protoliths, as well as a material contribution that is realized through various mechanisms of magma mixing. Mixing at the deep level is the most effective, resulting in the formation of significant volumes of increased basicity salic magmas. The petrogenetic role of contrasting magmas mixing at the mesoabyssal level of the earth's crust, as well as in hypabyssal conditions (mingling dikes), is not great, but these manifestations are the key argument in justifying the synchronicity of mafic and granitoid magmatism. Granitoids of Silicic Large Igneous Provinces (SLIPs) are characterized by a heterogeneous isotopic composition, generally corresponding to the parameters of the continental crust. The extremely high heterogeneity of spatially conjugate granitoids due to the mixing of silicic magmas formed through the melting of a small number of sources with contrasting isotopic compositions, including through mixing with magmas of mantle origin. Mafic rocks included in the granitoid provinces correspond to the isotopic composition of the enriched mantle (Angara-Vitim batholith) or indicate a significant contribution of contamination with continental crust material (Khangai area). The metallogeny of SLIPs is determined by the erosional section size and the crustal protoliths type, the metamorphism degree of which largely determines the initial fluid content of silicic magmas. The melting of highly metamorphosed ancient crustal protoliths produces relatively “dry” silicic melts, the melting of low-metamorphosed crustal sources leads to the formation of “aqueous” melts, the differentiation of which ends with pegmatite formation with rare metal mineralization. Non-subduction origin SLIPs formation is associated with the mantle plumes impact (in the form of synchronous basaltoid magmatism) on the heated crust of young orogenic regions, where tectonic processes ended no more than a few tens of Ma.

Emissiveness of technical cadmium and zinc

The results of an experimental study of the normal integral and normal spectral emissivity of technical cadmium and zinc are presented. The choice of the objects of study was due to the lack of literature data on the emissivity of these metals in the open press. The measurements were carried out by the absolute radiation method in an inert gas atmosphere. The results of the change in the intensity of the normal integral emissivity depending on the temperature with the fixation of the surge in the phase transition region are obtained. The normal spectral emissivity of solid polished metals in the melting region was investigated from 0.26 to 10.6 μm. A computational experiment was conducted using the Foote and Drude approximations.

Awakening of Maunaloa Linked to Melt Shared from Kīlauea’s Mantle Source

Abstract Maunaloa—the largest active volcano on Earth—erupted in 2022 after its longest known repose period (~38 years) and two decades of volcanic unrest. This eruptive hiatus at Maunaloa encompasses most of the ~35-year-long Puʻuʻōʻō eruption of neighboring Kīlauea, which ended in 2018 with a collapse of the summit caldera and an unusually voluminous (~1 km3) rift eruption. A long-term pattern of such anticorrelated eruptive behavior suggests that a magmatic connection exists between these volcanoes within the asthenospheric mantle source and melting region, the lithospheric mantle, and/or the volcanic edifice. The exact nature of this connection is enigmatic. In the past, the distinct compositions of lavas from Kīlauea and Maunaloa were thought to require completely separate magma pathways from the mantle source of each volcano to the surface. Here, we use a nearly 200-yr record of lava chemistry from both volcanoes to demonstrate that melt from a shared mantle source within the Hawaiian plume may be transported alternately to Kīlauea or Maunaloa on a timescale of decades. This process led to a correlated temporal variation in 206Pb/204Pb and 87Sr/86Sr at these volcanoes since the early 19th century with each becoming more active when it received melt from the shared source. Ratios of highly over moderately incompatible trace elements (e.g. Nb/Y) at Kīlauea reached a minimum from ~2000 to 2010, which coincides with an increase in seismicity and inflation at the summit of Maunaloa. Thereafter, a reversal in Nb/Y at Kīlauea signals a decline in the degree of mantle partial melting at this volcano and suggests that melt from the shared source is now being diverted from Kīlauea to Maunaloa for the first time since the early to mid-20th century. These observations link a mantle-related shift in melt generation and transport at Kīlauea to the awakening of Maunaloa in 2002 and its eruption in 2022. Monitoring of lava chemistry is a potential tool that may be used to forecast the behavior (e.g. eruption rate and frequency) of these adjacent volcanoes on a timescale of decades. A future increase in eruptive activity at Maunaloa is likely if the temporal increase in Nb/Y continues at Kīlauea.

The Influence of Using a Seismically Inferred Magma Reservoir Geometry in a Volcano Deformation Model for Soufrière Hills Volcano, Montserrat

AbstractVolcano deformation models contribute to hazard assessment by simulating magma system dynamics. Traditional magma reservoir pressure source shape assumptions often fail to replicate irregular, geophysically identified geometries. Uncertainties regarding the influence of reservoir geometry can limit the effectiveness of using deformation models to decipher unrest signals. Here, we aim to determine the feasibility of using a magma reservoir geometry directly derived from a seismic tomography survey in a volcano deformation model for Soufrière Hills Volcano, Montserrat. Three‐dimensional deformation models are created to simulate displacement using a pressure source geometry constrained from a low seismic velocity anomaly, inferred to be a region of partial melt, and contrasted against a traditional ellipsoid reservoir geometry. We also test a “hybrid” model combining a seismically inferred reservoir upper geometry and ellipsoidal base. Results of each model are evaluated against ground displacement observed on Montserrat from 2010 to 2022. Our results show that different reservoir geometries change the horizontal and vertical displacement fields across the island: the ellipsoid reservoir best reproduces vertical displacement magnitude, while the hybrid reservoirs best simulate horizontal displacement vectors and the region of maximum uplift. Overall, the ellipsoid‐shaped reservoir provides our best‐fit to the observed data, but we note this result could be biased due to prior years of optimization helping constrain the ellipsoid shape, size, and location. Our results show the potential for further use of geophysically constrained reservoir geometries in deformation modeling, and our methods could be applied to other deforming volcanoes worldwide.

Resolution enhancement of SMOS brightness temperatures: Application to melt detection on the Antarctic and Greenland ice sheets

Resolution enhancement of SMOS brightness temperatures: Application to melt detection on the Antarctic and Greenland ice sheets

Microcanonical Monte Carlo of Lennard-Jones microclusters.

A novel statistical mechanical methodology is applied to clusters of N ≤ 7 atoms. Exact statistical analogs for any energy derivative of entropy ∂mS/∂Em are used in rigorous microcanonical Monte Carlo simulations to vastly enlarge the pool of measurable thermodynamic properties relative to previous work. All analogs are given for two alternative partition functions of the microcanonical ensemble. Coarse grained energy distributions are used to establish the existence of melting transitions. LJ7, LJ5, and LJ4 are found to exhibit trimodal distributions, a feature not being reported before. Varieties of combinations of entropy derivatives are tested for a direct detection of the melting region. It is shown that for such a purpose, derivatives of at least fourth order are necessary.

A semi-analytical method based on the Green's function for the laser melting process of the metal materials

A semi-analytical method based on the Green's function for the laser melting process of the metal materials

Impact Craters on Earth with a Diameter of More than 200 km: Numerical Modeling

The three largest impact craters, the remains of which have been found on Earth to date, had diameters of about 200 km immediately after formation. The search for traces of larger impact structures continues. This paper presents the results of numerical modeling of the formation of terrestrial impact craters larger than those already found. It is shown that the inferred geothermal gradient significantly influences the initial geometry of the impact melt region, which may facilitate the search for the remains of deeply eroded ancient impact structures.

Summer sea ice melting enhances phytoplankton and dimethyl sulfide production

AbstractThe relationships among sea ice melting, phytoplankton assemblages, and the production of climate‐relevant trace gases in the Southern Ocean are gaining increasing attention from the scientific community. This is particularly true for dimethyl sulfide (DMS), which plays an important role in atmospheric chemistry by influencing the formation of sulfated aerosols with radiative impacts and constituting cloud condensation nuclei. In the current study, chlorophyll a (Chl a), DMS and its precursors dimethylsulfoniopropionate (DMSP), were quantified in the Weddell–Scotia Confluence (WSC) during the 2018 record ice extent minimum period. Mixed layer changes were found to be generally associated with spatial variation in sea ice melt, with the depth being six times deeper in ice‐free, well‐mixed regions than in seasonal ice‐melting zones. The surface Chl a concentration increased from ice‐free to ice‐melting regions with elevated sea ice meltwater percentages and drawdown surface nutrient concentrations. The concentrations of surface and depth‐integrated Chl a in the upper 150 m reached maxima in the ice‐melting region with the highest fraction of sea ice meltwater, illustrating that sea ice melting promoted the occurrence of phytoplankton blooms. The DMS and DMSP concentrations in the vicinity of the ice‐melting zone were approximately three times higher than those in the ice‐free waters. The observations of this study show that the regions of ice melting in the WSC were a zone of particularly high sea–air fluxes of DMS, which could significantly contribute to the atmospheric budget of DMS in the polar regions.

Investigation on heat transfer and fluid flow of a plasma arc in a plasma melting furnace: Model validation and parameter effects

Investigation on heat transfer and fluid flow of a plasma arc in a plasma melting furnace: Model validation and parameter effects