Melt Evolution Research Articles

Melt and fluid evolution in an upper-crustal magma reservoir, preserved by inclusions in juvenile clasts from the Kos Plateau Tuff, Aegean Arc, Greece

Pre- to syn-eruptive fluids released by the magmatic system forming the non-welded rhyolitic Kos Plateau Tuff ignimbrite, Greece, were characterized using fluid inclusions entrapped in quartz from granitic clasts entrained from the roof or walls of the feeding magma reservoir. This fluid was initially of intermediate density and relatively low salinity (3–11 wt% NaClequivalent). Following significant pressure drop(s), it separated into immiscible brine and CO2-bearing vapor occurring as texturally less mature inclusions. The transition from single- to two-phase-fluid occurred at magmatic conditions, as supported by high fluid inclusion homogenization temperatures (ca. 700 °C) and simultaneous trapping of fluid inclusions with silicate melt inclusions. The large recorded pressure drop together with texturally immature fluid inclusion shapes suggests a possible direct relation between the fluid phase change and the incipient 161 ka caldera-forming eruption. All inclusion types occur predominantly along (pseudo-) secondary trails in the granitic clasts, indicating efficient entrapment in microfractures formed at high crystallinity, as attested to by elevated concentrations of incompatible elements in the silicate melt inclusions.Fast quenching of the inclusions due to eruption prevented significant post-entrapment chemical modification, providing pristine samples of magmatic fluid compositions. Element concentrations in co-existing fluids and silicate melt were analyzed using laser ablation inductively-coupled plasma mass spectrometry and compared in view of element transporting capabilities and magmatic-hydrothermal ore formation. Economically important metals such as Cu, Zn, Mo, and W were extracted from the silicate melt by the fluid. In particular, Cu concentrations in the single-phase fluid in the range of 100–500 ppm agree well with previous experimental and modeling studies and, therefore, represent values expected for primary magmatic fluids. Most elements got further enriched in the brine upon phase separation, except Li, B, and As, which may have contributed significantly also to the vapor phase. Considering the similarity between vapor and intermediate-density fluid in terms of salinity, however, the metal-enriched brine phase only comprised a minor fraction of the bulk fluid.

Slab-controlled elemental–isotopic enrichments during subduction initiation magmatism and variations in forearc chemostratigraphy

Supra-subduction zone (SSZ) ophiolites formed in forearc settings and the Izu–Bonin–Mariana (IBM) in-situ forearc show conversions from normal mid-ocean ridge basalt (MORB) to boninitic affinities, which are widely interpreted as rules for the evolving chemical geodynamics of subduction initiation magmatism (SIM). Nevertheless, forearc sequence generated by subduction initiation need not always include boninitic rocks. Here we reconstruct a forearc chemostratigraphy without boninitic affinity based on the Central Palawan and Amnay (CPA) ophiolites of the west Philippines to show diversity in melt evolution of SIM. Zircon U–Pb dating on the MORB-type Amnay gabbros reveal a 10 m.y. of seafloor spreading from 33 to 23 Ma. These ages together with the progressively enriched zircon in-situ oxygen isotopes (δ18O= 1.62–10.1‰) and whole rock elemental and Nd–Hf isotopic signatures ([La/Yb]N= 0.19–3.45; Nb/Yb= 0.07–5.24; εNd= 2.1–10.2; εHf= 11.2–24.1) indicate that the depleted MORB mantle (DMM)-type source of the Amnay ophiolite was getting enriched by fluxing of aqueous slab fluid in the early stage followed by addition of adakitic and Nb-enriched slab melts in the later stage. This distinct mantle evolution together with higher εHf at a given εNd of the Amnay mafic samples than the contemporaneous South China Sea (SCS) oceanic samples do not support previous interpretation that the Amnay ophiolite was a fragment of the SCS. However, the 33–23 Ma Amnay ophiolite can be the younger part of the 34 Ma forearc-type Central Palawan ophiolite, and both (i.e. the CPA ophiolites) represent on-land fragments of the NW Sulu Sea. We propose that the 34–23 Ma CPA ophiolites and the NW Sulu Sea constitute forearc basin of the late Oligocene–middle Miocene island arc–backarc basin duo of the Cagayan Ridge and SE Sulu Sea, associated with subduction of the Cretaceous to Eocene Proto-SCS since 34 Ma. The CPA ophiolites lack boninite but show geochemical progression from normal to enriched MORB affinities, whose melt evolution differs from that of the IBM SIM. We attribute the differences in SIM and variations in forearc chemostratigraphy to the subduction of a younger slab with thick terrigenous sediment cover of the Proto-SCS versus an older slab with thin pelagic sediment cover of the Pacific Plate.

Through the impact glass: Insight into the evolution of melt at the Mistastin Lake impact structure

AbstractBy analyzing impact glass, the evolution of the impact melt at the Mistastin Lake impact structure was investigated. Impact glass clasts are present in a range of impactites, including polymict breccias and clast‐rich impact melt rock, and from a variety of settings within the crater. From the glass clasts analyzed, three petrographic subtypes of impact glass were identified based on their clast content, prevalence of schlieren, color, texture, and habit. Several alteration phases were also observed replacing glass and infilling vesicles; however, textural observations and quantified compositional data allowed for the identification of pristine impact glass. Although the various types of glasses show significant overlap in their major oxide composition, several subtle variations in the major oxide chemistry of the glass were observed. To investigate this variation, a least‐squares mixing model was implemented utilizing the composition of the glass and the known target rock chemistry to model the initial melt composition. Additionally, image analysis of the glass clasts was used to investigate whether the compositional variations correlated to textural difference in the lithologies. We propose that the textural and compositional dichotomy observed is a product of the evolution, assimilation, and emplacement of the glass. The dichotomy is reflective of the melt either being ballistically emplaced (group 2 glasses: occurring in melt‐poor polymict breccias at lowermost stratigraphic position outside the transient crater) or the result of late‐stage melt flows (group 1 glasses, occurring in melt‐bearing polymict breccias and impact melt rocks at higher stratigraphic positions outside the transient crater).

Genesis of Diamondiferous Rocks from Upper-Mantle Xenoliths in Kimberlite

The conditions of genesis of diamondiferous ultrabasic and basic rocks from xenoliths in kimberlite were studied by combining the data from analytical investigations of their mineral phases and experimental results of the study of melting relations in the diamond-forming mineral systems of the upper mantle. The compositions of minerals in some samples of metasomatized diamondiferous eclogite associated with diamond-free eclogite from kimberlite of the Udachnaya pipe (Yakutia) were studied for the first time. The new results obtained in addition to the literature data were applied for generalization of estimates of genetically important characteristics of the chemical compositions of garnets, Ca-clinopyroxenes, and omphacites from diamond-bearing peridotite, pyroxenite, and eclogite. As a result, it was found that quite “fresh” minerals of diamondiferous rocks have typomorphic differences from the same minerals of diamond-free upper-mantle rocks. At the same time, it is significant that the compositions of minerals from diamondiferous rocks and paragenetic inclusions in diamonds are identical. These peculiarities of mineralogy of diamondiferous rocks are genetically significant; based on the mantle–carbonatite theory of the origin of diamond and associated mineral phases, this provides support for the same physicochemical origin of diamonds, minerals of diamondiferous rocks, and paragenetic inclusions in diamonds. Finally, the following genetic conclusions are made. (1) Completely miscible silicate (±oxide)–carbonate melts with dissolved carbon are the parental medium in petrogenesis of diamondiferous ultrabasic and basic rocks. (2) The physicochemically consistent formation of diamondiferous rocks and paragenetic inclusions of peridotitic and eclogitic minerals in diamonds occurred in the common diamond-forming chambers/reservoirs of parental melts; diamond-free peridotite, pyroxenite, and eclogite were the host mantle rocks for such chambers. (3) The origin of continuous series of diamondiferous peridotite–pyroxenite–eclogite rocks is controlled by the fractional ultrabasic–basic evolution of parental melts with exhaustion of olivine and orthorhombic pyroxene via the peritectic reactions. (4) Ascending flows of kimberlite magmas destroyed the parental chambers and captured diamonds with inclusions, individual minerals, their intergrowths, diamondiferous ultrabasic and basic rocks; at the entrance and exit from the chambers, they captured differentiated diamond-free host rocks of the mantle as well. (5) With further ascent from the mantle to the Earth’s crust, the material of diamond-forming chambers and diamond-free mantle was mixed in convecting kimberlite magma and was transported from the mantle to cumulative crustal chambers. (6) Kimberlite magmas were gradually solidified in stationary cumulative chambers with the release of highly compressed fluids; with an increase of pressure up to the critical values, they intruded into the rocks of the roof and ejected kimberlite with xenoliths of diamondiferous and mantle rocks to the surface with the formation of explosion pipes.

The Generation of Trachytes and Comendites in the Subalkaline Differentiated Series, Sredinnyi Range, Kamchatka

The main subject of this article is research on the genetic relationships in the K–Na subalkaline series that occurs in the Belogolovsky volcanic center located in the back part of Sredinny Range. The differentiated rock series includes trachybasalts, trachyandesites, trachytes, comendite, trachytes, and comendites. Mass balance calculation and trace element modeling show that crystal fractionation is the main process in volcanic center evolution and the main fractionated mineral is feldspar. Trace element characteristics of rock-forming minerals (Fsp, Cpx, Bt, Ap, and Ol) obtained by LA–ICP–MS method allowed calculation of the “mineral/rock” partition coefficients for the Belogolovsky volcanic center genetic model representation to explain melt evolution. Genetic connections were established between trachyandesites, trachytes, comenditic trachytes and comendites, whereas no direct genetic connections between trachybasalts and trachyandesites were detected.

Unraveling the Effects of Melt–Mantle Interactions on the Gold Fertility of Magmas

The oxidation state of the Earth’s mantle and its partial melting products exerts a fundamental control on the behavior and distribution of sulphur and chalcophile and siderophile elements between the mantle and crust, underpinning models of ore deposit formation. Whether the oxidized nature of magmas in inherited from the asthenospheric mantle source or acquired during ascent and differentiation is vigorously debated, limiting our understanding of the mechanisms of extraction of sulphur and metals from the mantle. Here, we focused on the redox-sensitive behavior of sulphur in apatite crystallized from quenched alkaline basaltic melts preserved within a peridotite xenolith from the El Deseado Massif auriferous province in southern Patagonia. We took advantage of this unique setting to elucidate the redox evolution of melts during their ascent through the subcontinental lithospheric mantle, and grasp the inner workings of the Earth’s mantle during gold metallogenesis. Our data reveal that an initially reduced silicate melt (ΔFMQ -2.2 to -1.2) was oxidized to ΔFMQ between 0 and 1.2 during percolation and interaction with the surrounding peridotite wall-rock (ΔFMQ 0 to +0.8). This process triggered changes in sulphur speciation and solubility in the silicate melt, boosting the potential of the melt to scavenge ore metals such as gold. We suggest that large redox gradients resulting from the interaction between ascending melts and the surrounding mantle can potentially modify the oxidation state of primitive melts and enhance their metallogenic fertility. Among other factors including an enriched metal source and favorable geodynamic conditions, redox gradients in the mantle may exert a first-order control on the global-scale localization of crustal provinces endowed with gold deposits.

Controls on the explosive emplacement of diamondiferous kimberlites: New insights from hypabyssal and pyroclastic units in the Diavik mine, Canada

Kimberlites are mantle-derived magmas that either crystallise as hypabyssal intrusions, erupt explosively after rapid ascent to the surface, or less commonly form lava lakes and flows, thereby creating texturally distinct kimberlite units. Efforts to fully understand the processes responsible for the explosive eruption of kimberlite magmas have been hindered by the widespread alteration and crustal contamination of most volcaniclastic kimberlites. To address this issue, we have undertaken a detailed petrographic and mineral chemical study of fresh (i.e. minimally altered) pyroclastic and hypabyssal kimberlites (HK) from the ca. 55-56 Ma A154 North and South kimberlite pipes in the Diavik Mine (Lac de Gras, Canada). These localities host exceptionally fresh kimberlites and are therefore ideally suited to this study.Kimberlite emplacement at A154 North and South initiated with the intrusion of hypabyssal kimberlite (external dykes), and was followed by the explosive formation of kimberlite pipes and volcaniclastic kimberlite infill. Subsequent kimberlite magmas intruded the volcaniclastic kimberlite units forming multiple cross-cutting, internal dykes. The studied volcaniclastic units feature abundant rounded magmaclasts and massive textures, suggestive of primary deposits. These units are classified as pyroclastic kimberlites (PK).Pyroclastic and hypabyssal kimberlite units at Diavik exhibit subtle mineral compositional differences. Samples from both internal HK units and PK units feature identical compositions for liquidus olivine rims (Mg# = 90.5 ± 0.1 and 90.7 ± 0.2, respectively), with a marginally lower Mg# of 90.2 ± 0.2 in olivine rims from the external HK dykes. Similarly, early-formed chromite compositions are the same for internal HK and PK units (Cr# = 79.1 ± 3.4 and 78.3 ± 5.7; Mg# = 60.0 ± 1.3 and 60.0 ± 2.2), but, differ in the external HK units (Cr# = 86.9 ± 2.7; Mg# = 52.8 ± 1.9). The internal HK and PK units also exhibit lower carbonate contents than the internal HK units. These compositional differences indicate that the external dykes were probably derived from slightly different primitive melt compositions to those parental to the internal HK and PK units. Spinel evolutionary trends from chromite to magnesian ulvӧspinel-magnetite (MUM) compositions are indistinguishable in internal HK and PK samples (Fe3+# = 47.2 ± 5.8 and 49.7 ± 9.3; Cr# = 25.7 ± 11.0 and 17.0 ± 14.0). These results demonstrate that the primitive melt compositions and early magmatic evolution processes are identical for the internal kimberlite units, regardless of whether the kimberlite melts erupted explosively or were emplaced as shallow intrusions. However, magmaclasts in the PK units contain higher abundances of phlogopite (<52 vol. %) and lower quantities of carbonate (<4 vol. %) than the groundmass of the hypabyssal kimberlite samples (<2 vol. % and 25–65 vol. %, respectively). This indicates that the explosively erupted magmas featured higher H2O/CO2 ratios. In contrast, abundant carbonates, including dolomite, in the internal HK samples indicate that CO2, and therefore low H2O/CO2 ratios, were retained during the emplacement of this magma, which likely prevented phlogopite crystallisation. Lower K and Rb whole-rock compositions for internal HK samples compared to PK samples, are attributed to the removal of these components in late-stage kimberlitic fluids, as indicated by hydrothermal alteration of the adjacent volcaniclastic kimberlite units. The above results clearly rule out variations in primitive melt composition and melt evolution trajectories as a primary control on the explosive behaviour of the kimberlite magmas at Diavik. Controls on kimberlite explosivity at Diavik are likely due to external factors, such as local stress regimes, the availability of groundwater (i.e. phreatomagmatism) and differing magma supply rates.

A genetic story of olivine crystallisation in the Mark kimberlite (Canada) revealed by zoning and melt inclusions

Elucidating the composition of primary kimberlite melts is essential to understanding the nature of their source, petrogenesis, rheology, transport and ultimately the origin of diamonds. Kimberlite rocks are typically comprised of abundant olivine (~25–60 vol%), which occurs as individual grains of variable size and morphology, and includes xenocrysts and zoned phenocrysts. Zoning patterns and inclusions in olivine can be used to decipher the petrogenetic history of kimberlites, starting from their generation in the mantle through to emplacement in the crust. This study examines well-preserved, euhedral, zoned olivine crystals from the Mark kimberlite (Lac de Gras, Canada). Olivine typically consists of xenocrystic cores, which are homogeneous in composition but vary widely between grains (Fo88.1–93.6). These cores are in turn surrounded by (in order of crystallisation) magmatic rims and Mg-rich rinds (Fo95.3–98.1). In addition, we document a new type of olivine zone (‘outmost rind’) that overgrows Mg-rich rinds.Crystal and melt/fluid inclusions are abundant in olivine and preserve a record of kimberlite melt evolution. For the first time in the studies of kimberlite olivine, we report primary melt inclusions hosted in Mg-rich olivine rinds. In addition, we observe that pseudosecondary melt/fluid inclusions are restricted to interior olivine zones (cores, rims) and are considered to have formed prior to rind formation. Pseudosecondary melt/fluid inclusions are inferred to have been entrapped at depth, as evidenced by measured densities in thermometric experiments of CO2 and decrepitation haloes, indicating a minimum entrapment pressure of ~200–450 MPa (or ~6–15 km). Both primary and pseudosecondary melt inclusions in olivine have daughter minerals dominated by CaMg and K-Na-Ba-Sr-bearing carbonates, K-Na-chlorides along with subordinate silicates (e.g., phlogopite, monticellite), Fe-Mg-Al-Ti-spinel, perovskite, phosphates and sulphates/sulphides and periclase. In addition to phases reported in primary melt inclusions, pseudosecondary melt inclusions contain more diverse and exotic daughter mineral assemblages, where they contain phases such as tetraferriphlogopite Ba- or K-sulphates, kalsilite and Na-phosphates. The daughter mineral assemblages are consistent with a silica-poor, alkali dolomitic carbonatite melt. We demonstrate that the different types of inclusions in olivine can assist in constraining the timing of multi-stage olivine growth and the composition of the crystallising melt.The large variance in olivine zoning patterns, morphologies and Ni distribution (i.e. both coupling with and decoupling from Fo) indicates that olivine in the studied Mark kimberlite samples represent an accumulation of olivine, where olivine was derived from successive stages of the ascending magma and/or from multiple, but related pulses of magma. Primary and pseudosecondary melt/fluid inclusions in olivine indicate that a variably differentiated silica-poor, halogen-bearing, alkali-dolomitic melt crystallised and transported olivine in the Mark kimberlite.

Anatomy of the magmatic plumbing system of Los Humeros Caldera (Mexico): implications for geothermal systems

Abstract. Understanding the anatomy of magma plumbing systems of active volcanoes is essential not only for unraveling magma dynamics and eruptive behaviors but also to define the geometry, depth, and temperature of the heat sources for geothermal exploration. The Pleistocene–Holocene Los Humeros volcanic complex is part of the eastern Trans-Mexican Volcanic Belt (central Mexico), and it constitutes one of the most important exploited geothermal fields in Mexico with ca. 90 MW of produced electricity. With the aim to decipher the anatomy (geometry and structure) of the magmatic plumbing system feeding the geothermal field at Los Humeros, we carried out a field-based petrological and thermobarometric study of the exposed Holocene lavas. Textural analysis, whole-rock major-element data, and mineral chemistry are integrated with a suite of mineral-liquid thermobarometric models. Our results support a scenario characterized by a heterogeneous multilayered system, comprising a deep (depth of ca. 30 km) basaltic reservoir feeding progressively shallower and smaller discrete magma stagnation layers and batches, up to shallow-crust conditions (depth of ca. 3 km). The evolution of melts in the feeding system is mainly controlled by differentiation processes through fractional crystallization (plagioclase + clinopyroxene + olivine + spinel). We demonstrate the inadequacy of the existing conceptual models, where a single voluminous melt-controlled magma chamber (or “Standard Model”) at shallow depths was proposed for the magmatic plumbing system at Los Humeros. We instead propose a magmatic plumbing system made of multiple, more or less interconnected, magma transport and storage layers within the crust, feeding small (ephemeral) magma chambers at shallow-crustal conditions. This revised scenario provides a new configuration of the heat source feeding the geothermal reservoir at Los Humeros, and it should be taken into account to drive future exploration and exploitation strategies.

Broadband albedo of Arctic sea ice from MERIS optical data

Abstract. Arctic summer sea ice experiences rapid changes in its sea-ice concentration, surface albedo, and the melt pond fraction. This affects the energy balance of the region and demands an accurate knowledge of those surface characteristics in climate models. In this paper, the broadband albedo (300–3000 nm) of Arctic sea ice is derived from MEdium Resolution Imaging Spectrometer (MERIS) optical swath data by transforming the spectral albedo as an output from the Melt Pond Detector (MPD) algorithm with a newly developed spectral-to-broadband conversion (STBC). The new STBC replaces the previously applied spectral averaging method to provide a more accurate broadband albedo product, which approaches the accuracy of 0.02–0.05 required in climate simulations and allows a direct comparison to broadband albedo values from climate models. The STBC is derived empirically from spectral and broadband albedo measurements over landfast ice. It is validated on a variety of simultaneous spectral and broadband field measurements over Arctic sea ice, is compared to existing conversion techniques, and performs better than the currently published algorithms. The root-mean-square deviation (RMSD) between broadband albedo that was measured and converted by the STBC is 0.02. Other conversion techniques, the spectral averaging method and the linear combination of albedo values from four MERIS channels, result in higher RMSDs of 0.09 and 0.05, respectively. The improved MERIS-derived broadband albedo values are validated with airborne measurements. Results show a smaller RMSD of 0.04 for landfast ice than the RMSD of 0.07 for drifting ice. The MERIS-derived broadband albedo is compared to broadband albedo from ERA5 reanalysis to examine the albedo parameterization used in ERA5. Both albedo products agree over large scales and in temporal patterns. However, consistency in point-to-point comparison is rather poor, with differences up to 0.20, correlations between 0.69 and 0.79, and RMSDs in excess of 0.10. Differences in sea-ice concentration and cloud-masking uncertainties play a role, but most discrepancies can be attributed to climatological sea-ice albedo values used in ERA5. They are not adequate and need revising, in order to better simulate surface heat fluxes in the Arctic. The advantage of the resulting broadband albedo data set from MERIS over other published data sets is the accompanied data set of available melt pond fraction. Melt ponds are the main reason for the sea-ice albedo change in summer but are currently not represented in climate models and atmospheric reanalysis. Additional information about melt evolution, together with accurate albedo retrievals, can aid the challenging representation of sea-ice optical properties in those models in summer.

How do diamonds grow in metal melt together with silicate minerals? An experimental study of diamond morphology

Abstract. The origin and evolution of metal melts in the Earth's mantle and their role in the formation of diamond are the subject of active discussion. It is widely accepted that portions of metal melts in the form of pockets can be a suitable medium for diamond growth. This raises questions about the role of silicate minerals that form the walls of these pockets and are present in the volume of the metal melt during the growth of diamonds. The aim of the present work was to study the crystallization of diamond in a complex heterogeneous system: metal-melt–basalt–carbon. The experiments were performed using a multianvil high-pressure apparatus of split-sphere type (BARS) at a pressure of 5.5 GPa and a temperature of 1500 ∘C. The results demonstrated crystallization of diamond in metal melt together with garnet and clinopyroxene, whose chemical compositions are similar to those of eclogitic inclusions in natural diamond. We show that the presence of silicates in the crystallization medium does not reduce the chemical ability of metal melts to catalyze the conversion of graphite into diamond, and, morphologically, diamond crystallizes mainly in the form of a cuboctahedron. When the content of the silicate material in the system exceeds 5 wt %, diamond forms parallel-growth aggregates, but 15 wt % of silicate phases block the crystallization chamber, preventing the penetration of metallic melt into them, thus interrupting the growth of diamond. We infer that the studied mechanism of diamond crystallization can occur at lower-mantle conditions but could also have taken place in the ancient continental mantle of the Earth, under reducing conditions that allowed the stability of Fe–Ni melts.

The role of accreted continental crust in the formation of granites within the Alpine style continental collision zone: Geochemical and geochronological constrains from leucogranites in the Çataldağ Metamorphic Core Complex (NW Turkey)

The recently discovered Çataldağ Metamorphic Core Complex (ÇMCC) of Eo-Oligocene age is situated in NW Turkey, which is a part of the Alpine collisional belt. The footwall of the ÇMCC consists of a granite-gneiss-migmatite complex (GGMC) with a domal structure. Here, we document new major-trace element geochemistry, Sr-Nd-Pb isotope characteristics and Ti-in-zircon thermometry data from granites and syn-plutonic mafic dykes that are connected to the gneiss-migmatite dome of ÇMCC, and discuss granitic melt evolution within the context of the syn-to post-collisional evolution of the western Anatolian orogenic crust. Granites of the GGMC include both peraluminous garnet-bearing leucogranite and two-mica granite that emplaced from 32 to 35 Ma. Both types of leucogranite are enriched in light rare earth elements (Rb, U, K, Pb) and depleted in HFSE (Nb, Ta, Zr, Ti). Their 87Sr/86Sr, 206Pb/204Pb and 207Pb/204Pb initial isotope values range from 0.7094 to 0.7113, 18.79 to 18.91, and 15.71 to 15.73, respectively, and εNd(33) values vary between −5.13 and − 7.79. On the other hand, mafic dykes show similar isotopic characteristics (87Sr/86Sr(33) = 0.7055, εNd(33) = −1.8 and 206Pb/204Pb = 18.8) to enriched mantle melts. Geochemical modelling shows that the granites have dominant crustal melt component (85–70%) and a minor mantle component (<30%). According to partial melting modelling and Ti-in-zircon thermometer calculations, granitic melt was formed by water-absent muscovite dehydration melting of a micaschist source (a melt fraction of max. 35%) at ≥7–10 kb and 739–840 °C. Whole rock geochemistry, isotopic characteristics and inherited zircon chronology, combined with the geology of the region, indicate that granitic melts were derived by partial melting of Anatolide-Tauride crustal units that were underthrusted below the Sakarya Continent along the İzmir-Ankara Suture Zone. On the other hand, the source of the syn plutonic mafic dykes emplaced in the core of the ÇMCC is inferred to derived from enriched mantle (EM II) that lay beneath the western Anatolian orogenic crust. We infer that partial melting and melt migration to produce leucogranites are most probably related to thermal weakening and partial removal of western Anatolian young orogenic lithosphere during the transitional phase between the latest phase of collision and the earliest phase of extension, in the Eo-Oligocene.

Genesis and evolution of the mantle melts of the devonian mafic-ultramafic rocks from the Eastern Azov region (Dnieper-Donetsk rift, Ukraine) based on the clinopyroxene geochemistry study

The Devonian magmatic association of the Eastern Azov region, which is part of the Pripyat-Dnieper-Donetsk rift zone, was studied. The association includes gabbroids, peridotites, pyroxenites, and lamprophyre dikes of the Pokrovo-Kireevsky massif (PKM) and picrites, picrobasalts and basalts of the Anton-Taramskaya suite (ATS). The clinopyroxenes of different generations from the micaceous PCM gabbro and the alkaline ATS picrite were studied. It was obtained the information on the mantle source composition and the evolution of melts, who determined the close spatial-temporal location of kimberlites, basites, ultramafic rocks, including alkaline ones, in the Eastern Azov region.&#x0D; Clinopyroxenes from micaceous gabbro are composed of Cpx1 (Mg# = 0.870.88) or Сpx2 (Mg# = 0.800.81) cores and Cpx3 external zones (Mg# = 0.700.76). Clinopyroxenes in alkaline picrite are composed of Сpx2 cores (Mg # = 0.800.84) and external Cpx3 zones (Mg# = 0.710.78). The multielement spectra of clinopyroxenes are generally dome-shaped in nature, with enrichment with LREE, depletion of Ba, Nb, TREE, Zr-Hf negative anomaly, a negative Sr-anomaly appears in Cpx2 and Cpx3 also. The resulting compositions of the model melt for Сpx2 from the micaceous gabbro are very close to the composition of this gabbro, and the compositions of the model melt for Cpx2 from the alkaline picrite coincide with those of this picrite. The high Mg# value and concentrations of Cr in Cpx1 cores indicate that the earliest weakly differentiated composition close to the primary could serve as the equilibrium melt. The presence in the Cpx1 geochemical spectra of a negative Zr-Hf anomaly at ZrPM HfРМ may be evidence of the origin of melts that once contained these clinopyroxenes, due to the melting of metasomatized, possibly carbonated garnet-contained peridotites. Probably, the Cpx1 cores are relics of phenocrysts crystallized from the earliest melt during the formation of the PCM and the ATS.&#x0D; An important feature of the Eastern Azov rocks is a very high content of Ti (up to 7.3 wt.% TiO2) in the high-Mg (Mg# = 0.480.65) and deep (CaO/Al2O3 0.8) melts, which formed picrobasalts and lamprophyres. The geochemical features of the early Cpx1 cores compared with the geochemistry of clinopyroxenes from ilmenite-containing mantle metasomatites are consistent with the assumption that carbonated ilmenite-containing peridotites, possibly also phlogopite-containing (PIC), are the source of ultrahigh-Ti primary melts for the Eastern Azov lamprophyres.

Petrological-geochemical characteristics of lavas, sources and evolution of magmatic melts of the Kazbek neovolcanic center (Greater Caucasus)

The results of petrological-geochemical and isotope-geochemical studies of the Late Pleistocene-Holocene lavas of the Kazbek Neovolcanic Center, one of the largest centers of youngest magmatism in the Greater Caucasus, are presented.&#x0D; It has been established that the volcanic rocks of the Kazbek center arise a continuous compositional series basaltic (trachy-)andesites(trachy-)andesitesdacites with a predominance of calc-alkaline intermediate and moderately-acid lavas. The obtained results indicate that the processes of fractional crystallization and mixing of melts had a leading role in the petrogenesis of the rocks. The crustal assimilation was of limited importance; its influence is noticeable only in the rocks of the earliest and late pulses of magmatic activity within the Kazbek center. The common crustal lithologies participated in the assimilation were presented by metamorphosed Jurassic sediments (mainly shales and sandstones), forming the foot of the Kazbek center, and Mesozoic mafic metamorphosed volcanites very rarely. The specific features of AFC processes during the development of the studied magmatic system (including the presence of noticeable amount of water in the melt, the leading role of Amp in the cumulus and the absence of Pl fractionation) led to the appearance of dacitic lavas with geochemical signs of adakites as an evolutional end-member.&#x0D; The volcanic rocks of the Kazbek center are derived from trachybasalt magmas, the source of which was presented by the mantle reservoir of OIB-type. Recent and previously published results of studies of the Neogene-Quaternary magmatism manifested within the Greater Caucasus show that the main petrological and geochemical characteristics of this regional mantle reservoir remained constant from the end of the Miocene to the present time.

Geodynamic nature of magmatic sources of North-West Pacific: an interpretation data on isotope composition of Sr and Nd in rocks dredged at Stalemate ridge, Ingenstrem depression, and Shirshov Rise

First data on isotope composition of Sr and Nd in rocks dredged at different areas belong to lithosphere of the NW Pacific are present. All samples examined were obtained from NW termination of Stalemate Ridge (NW Pacific) and Central part of Shirshov Rise (Western Bering Sea). Results of conducted study allow sure enough to judge on geodynamic affinity of the central segment of Shirshov Rise. Mafic-ultramafic rocks dredged here originated due evolution of magmatic melt formed by partial melting of source parental for MORB belongs to mantle wedge perhaps. Thus, this interpretation means that Shirshov Rise is remnant Back-Arc Spreading Center. Data on petrology and isotope chemistry of rocks from Stalemate magmatic assemblage demonstrate geochemical heterogeneity of their possible magmatic sources. The presented data allow to assume participation in magmatism of this region of NW Pacific source that responsible for formation of most older volcanic seamounts from NW Termination of Hawaiian-Emperor volcanic chain. There is petrographic similarity between rock assemblage recovered at NW Stalemate and plutonic rocks composed of xenoliths from volcanic effusions of Aleutian Island Arc exists. Considering the scarcity of existing information about the structure of the lithosphere in the NW Pacific it is possible to assume with caution the participation in the construction of the oceanic slope of the Aleutian Trench and the adjacent segment of the Stelmate Ridge fragments of Aleutian Arc basement.

Chlorine and felsic magma evolution: Modeling the behavior of an under-appreciated volatile component

Research on magmatic Cl has proven useful for understanding melt evolution, degassing, and other igneous processes. Magmatic Cl behavior varies strongly with its solubility in melt, and Cl solubility and its partitioning between melts and fluids vary with the Cl content of the system, melt composition, pressure, and the abundance of oxidized magmatic sulfur. Given these relationships and given that they differ from other magmatic volatiles, Cl can provide unique insights on magma evolution. We present a new method of interpreting melt Cl concentrations that are normalized to their calculated Cl solubilities, and the most accurate results apply to solubilities computed at 200 MPa due to insufficient experimental data for other pressures. We apply the new method to compositional data for more than 3500 dacitic to rhyolitic melt inclusions and matrix glasses, representing 64 felsic igneous systems, to demonstrate how the behavior of Cl during magmatic, magmatic-hydrothermal, and degassing processes can be more accurately interpreted.Variations in Cl for most of the 64 systems agree with modeled Cl behavior indicative of melt evolution dominated by fractional crystallization of fluid(s)-saturated melts, and the majority of these systems were apparently saturated in fluid(s) well before melt inclusion entrapment. Comparison of Cl solubility-normalized Cl concentrations of these glasses with modeled results identifies magmas saturated in hydrosaline liquid ± vapor at pressures as high as 600 MPa. Modeling of pressure reductions from 600 down to 20 MPa distinguishes other magmas that exsolved hydrosaline liquid as magmas ascend to shallower depths. This new approach also supports computation of Cl concentrations of magmatic fluids at 200 MPa, for each of the >3500 glasses, and shows how the Cl contents of fluids vary with the (fluid/melt) mass ratio. For example, Cl contents of magmatic fluids range from 0.3 to nearly 70 wt.% at fluid/melt mass ratios of 2 × 10−3, and from 0.3 to a maximum of only 11 wt.% Cl for fluid/melt mass ratios of 4.2 × 10−2.Compositional trends in the glass data show either increasing Cl contents of residual melt, essentially no change of Cl in melt, or decreasing Cl contents of aliquots of residual melt with progressive melt evolution. This method identifies melts that have assimilated magmatic or externally sourced hydrosaline liquids. Plots of (measured Cl in melt/modeled solubility of Cl in melt; Cl[Me/Mo]) versus the Larsen melt differentiation index show minimal dispersion for the least-evolved dacitic melts and increasing dispersion with melt evolution to rhyolitic compositions. Increased dispersion may be a consequence and indication of equilibrium or non-equilibrium degassing and/or assimilation of hydrosaline liquid.

Inhomogeneous microstructure and its evolution of laser melting deposited 24CrNiMo steel: From single-track to bulk sample

The microstructure of 24CrNiMo steel samples fabricated via laser melting deposition (LMD) is inhomogeneous, and has not received enough attention. To study the inhomogeneous microstructure and its evolution rule during LMD, single-track, single-layer, and multi-layer samples were fabricated via LMD. The microstructure, grain size, and texture intensity of the samples were analysed by optical microscopy, scanning electron microscopy, and electron backscatter diffraction. In addition, the hardness and strength were measured, and the evolution of the temperature field was simulated using the finite element method. The results indicate that heat accumulation during the LMD process caused the substrate temperature to rise. The higher the substrate temperature, the lower the cooling rate of the molten pool. Thermal accumulation not only altered the rules of microstructure change, but also caused grain refinement and weakened the texture. In addition, the thermal cycle caused phase transformation of the previously formed microstructure, resulting in grain refinement and weakening the texture. Thermal cycle and thermal accumulation caused the microstructure of multi-track samples to become inhomogeneous. The uneven microstructure made the hardness distribution irregular, and caused the macro-mechanical properties of the LMD 24CrNiMo sample to fluctuate in a relatively large range. In this study, the microstructure evolution of the LMD process was comprehensively traced, and the formation process of inhomogeneous microstructure was revealed.

Petrological geodynamics of mantle melting III. AlphaMELTS + multiphase flow: The effect of water

The influence of water is evaluated in this last contribution of a series aiming to study the petrological and dynamic evolution of mantle melting. Water is considered to be either a chemical component in the melt or solid assemblage but it can also be present as a pure water phase in a oversaturated environment. A three-phase-flow model was developed for this purpose.Only a limited set of conditions has been applied to the 1-D upwelling mantle column. A range of fixed temperatures (1150–1450 °C) and water contents in the solid mantle (0, 0.02 wt.%, 0.2 ​wt.%) have been imposed at the entry point (120 ​km deep) for the two melting models introduced in the previous installments, dynamic equilibrium melting (DEM) and dynamic fractional melting (DFM) model.As expected, for a given temperature at the base of the mantle column, the depth of the first melt formation increases with higher water content in the mantle. After the first melt is created, very negligible amount of melt is formed over a certain depth interval which approximately ends at the depth where the first melting of the dry mantle would take place. However melt is present as a dynamic phase thorough the entire region regardless whether the DEM or DFM model has been applied.Under a quasi-steady state regime, the melt and residual mantle compositions vary significantly over depth, depending on the conditions imposed to the model (DEM, DFM, bottom temperature and water content). Several distinctions can be made at the extraction point (top of the mantle column ​= ​15 ​km deep). For DEM and DFM models at this lowest depth, the most influential factor affecting the melt composition after the quasi-steady state condition has been reached is the temperature at the base of the column. In general, for a high temperature model, the input water in the mantle does not seem to play a significant role on the bulk composition of the melt (except for the water content in melt). But at low temperature water does have some noticeable influence on the variation of some chemical components in melt (SiO2, Fe2O3, CaO, Na2O at T ​= ​1250 °C or lower). A similar conclusion can be made also for the residual mantle composition. The presence of a dynamic free water phase is detected only in absence of melt or in coexistence with a melt phase when the mantle is relatively cold (bottom temperature ≤1250 °C) and the input water content at the base of the model is relatively high (0.2 ​wt.%).Complete output data for several numerical simulations and six animations illustrating various melting models are available following the instructions in the supplementary material.

A research on the surface morphology, microstructure evolution and wear property of selective laser melting Al2O3/P20 composites

The Al2O3/P20 composites were successfully manufactured by selective laser melting (SLM) from powder mixture of Al2O3 and P20 mold steel with different Al2O3 contents (0.5 wt%, 1 wt%, 2 wt%) in this work. The surface morphology analysis indicated that Al2O3 particles were partially or fully melted for agglomerates during the SLM process with segregating between contiguous molten tracks. The model of Al2O3 diffusing during the SLM process was built for illustrating the generated mechanism of Al2O3 agglomerates. Moreover, the densification behavior of specimens became poor (the relative density declined from 99.3% to 94.2%) as the Al2O3 contents increased. The microstructure within samples had some obvious variations including coarsening martensite microstructure, tempering microstructure transformation, reverted austensite and precipitation of fine carbide particles. The result of Rockwll hardness test manifested that 1 wt% obtained the maximum value of 57.6 HRC, while 2 wt% had the minimum value of 45.9 HRC. Tribological test revealed that coefficient of friction (COF) and wear rate significantly declined when the Al2O3 contents were 1 wt% and 2 wt%, which emphasized the superior wear resistance property.

Improved PCM melting in a thermal energy storage system of double-pipe helical-coil tube

This study proposes the use of a double-pipe helical-coiled tube as an innovative well-performing phase change material (PCM) containment design for latent heat thermal energy storage (LHTES) systems. A 3D numerical model considering the convection effects during PCM melting is built and successfully validated via experiments. To assess the new LHTES design, the melting evolution of PCM in horizontal and vertical straight double-pipe LHTES systems with the same surface area is initially simulated and compared with the new same-size LHTES system. Thereafter, the thermal performance of the double-pipe helical-coil storage has been intensively investigated under various operational conditions. Results reveal that the thermal performance of the double-pipe helical-coil LHTES during the PCM melting phase is spurious compared with that of others. The required saving in the PCM melting time is approximately 25.7% and 60% for the horizontal and vertical straight double-pipe LHTES systems, respectively. Moreover, results show that the coil pitch has a remarkably impact on the total PCM melting time in the double-pipe helical-coiled tube, however the optimum coil pitch is 2 OD. The analysis also reveals that the initial temperature and Reynolds number (Re) of heat transfer fluid (HTF) are other factors that significantly affect the PCM melting process.