Modelling of water jet impact on molten metal

Splashes of high-temperature melt spreading over a water pool bottom can be a reason for the formation of a zone where melt, water and steam are mixed, providing conditions for powerful steam explosions. The paper considers the formation of melt splashes arising from the impact of a water jet on the surface of the melt. Numerical simulations are performed in 3D formulation, using the VOF method and an improved phase change model. The evolution of melt surface following the water jet impact is demonstrated, including the formation of a cavern, a primary melt splash known as the crown, as well as a secondary splash following the collapse of the cavern, known as the cumulative jet. Parametric study for the melt splash height dependence on the water jet geometry and velocity is carried out. The results of numerical analysis are discussed from the point of view of the similarity with respect to the momentum and kinetic energy of water jet. The significance of the results for the steam explosion problem is discussed.

Mixing between chemically variable primitive basalts creates and modifies crystal cargoes

Basaltic crystal cargoes often preserve records of mantle-derived chemical variability that have been erased from their carrier liquids by magma mixing. However, the consequences of mixing between similarly primitive but otherwise chemically variable magmas remain poorly understood despite ubiquitous evidence of chemical variability in primary melt compositions and mixing-induced disequilibrium within erupted crystal cargoes. Here we report observations from magma–magma reaction experiments performed on analogues of primitive Icelandic lavas derived from distinct mantle sources to determine how their crystal cargoes respond to mixing-induced chemical disequilibrium. Chemical variability in our experimental products is controlled dominantly by major element diffusion in the melt that alters phase equilibria and triggers plagioclase resorption within regions that were initially plagioclase saturated. Isothermal mixing between chemically variable basaltic magmas may therefore play important but previously underappreciated roles in creating and modifying crystal cargoes by unlocking plagioclase-rich mushes and driving resorption, (re-)crystallisation and solid-state diffusion.

Compositional Variations of Spinels from Ultramafic Lamprophyres of the Chadobets Complex (Siberian Craton, Russia)

Ultramafic lamprophyres (UMLs) are mantle rocks that provide important information about the composition of specific carbonate–silicate alkaline melts in the mantle as well as the processes contributing to their origin. Minerals of the spinel group typically occur in UMLs and have a unique “genetic memory.” Investigations of the spinel minerals from the UMLs of the Chadobets complex show the physicochemical and thermodynamic features of the alkaline rocks’ crystallization. The spinels of these UMLs have four stages of crystallization. The first spinel xenocrysts were found only in damtjernite pipes, formed from mantle peridotite, and were captured during the rising of the primary melt to the surface. The next stages of the spinel composition evolution are related to the high-chromium spinel crystallization, which changed to a high-alumina composition. The composition then changed to magnesian ulvöspinel–magnetites with strong decreases in the Al and Cr amounts caused by the release of carbon dioxide, rapid temperature changes, and crystallization of the main primary groundmass minerals such as phlogopite and carbonates. Melt inclusion analyses showed the predominance of aluminosilicate (phlogopite, clinopyroxene, and/or albite) and carbonate (calcite and dolomite) daughter phases in the inclusions that are consistent with the chemical evolution of the Cr-spinel trend. The further evolution of the spinels from magnesian ulvöspinel–magnetite to Ti-magnetite is accompanied by the formation of atoll structures caused by resorption of the spinel minerals.

Modeling of Olivine and Clinopyroxene Fractionation in Intracontinental Alkaline Basalts: A Case Study from the Carpathian-Pannonian Region

Besides mantle peridotites primary basaltic melts are the best tool to investigate upper mantle petrology and geochemistry. However, de facto primitive melts are hard to found, as basaltic melts usually go through a fractionation process during their ascent towards the surface. Most primary melt calculators are based on the major or trace element compositions of olivine-phyric ocean island basalts and peridotites and are less accurate if clinopyroxene fractionation occurred. In this chapter a new fractionation modeling method of alkaline basalts will be introduced, which has been published earlier only in Hungarian. Olivine ± clinopyroxene fractionation of four basaltic volcanoes have been modeled from different Miocene-Quaternary volcanic fields from the Carpathian-Pannonian Region (Stiavnica (Selmec) VF, Novohrad-Gemer (Nógrád-Gömör) VF, Perşani Mts. (Persányi Mts.) VF and from the Lucaret-Sanoviţa (Lukácskő-Sziklás) volcano.

Formation Mechanism of the Velyka Vyska Syenite Massif (Korsun-Novomyrhorod Pluton, Ukrainian Shield) Derived from Melt Inclusions in Zircon

The formation of leucosyenites in the Velyka Vyska syenite massif was provoked by the liquation layering of magmatic melt. This assumption is based on the presence of two primary melt inclusions of different chemical composition in zircon crystals from Velyka Vyska leucosyenites. They correspond to two types of silicate melts. Type I is a leucosyenite type that contains high SiO2 concentrations (these inclusions dominate quantitatively); type II is a melanosyenite type that contains elevated Fe and smaller SiO2 concentrations. The liquation layering of magmatic melt was slow because the liquates are similar in density; leucosyenite melt, which is more abundant than melt of melanosyenite composition, displays greater dynamic viscosity; the initial sizes of embryos of melanosyenite composition are microscopic. Sulphide melt, similar in composition to pyrrhotite, was also involved in the formation of the massif. Zircon was crystallized at temperatures over 1300°С, as indicated by the homogenization temperatures of primary melt inclusions. The REE distribution spectra of the main parts (or zones,) of zircon crystals from the Velyka Vyska massif are identical to those of zircon from the Azov and Yastrubets syenite massifs with which high-grade Zr and REE (Azov and Yastrubets) ore deposits are associated. They are characteristic of magmatically generated zircon. Some of the grains analyzed contain rims that are contrasting against the matrix of a crystal, look dark-grey in the BSE image and display flattened REE distribution spectra. Such spectra are also typical of baddeleyite, which formed by the partial replacement of zircon crystals. The formation of a dark-grey rim in zircon and baddeleyite is attributed to the strong effect of high-pressure СО2-fluid on the rock. The formation patterns of the Velyka Vyska and Azov massifs exhibit some common features: (а) silicate melt liquation; (b) high ZrO2 concentrations in glasses from hardened primary melt inclusions; (c) the supply of high-pressure СО2-fluid flows into Velyka Vyska and Azov hard rocks. Similar conditions of formation suggest the occurrence of high-grade Zr and REE ores in the Velyka Vyska syenite massif.

Kimberlite genesis from a common carbonate-rich primary melt modified by lithospheric mantle assimilation

Quantifying the compositional evolution of mantle-derived melts from source to surface is fundamental for constraining the nature of primary melts and deep Earth composition. Despite abundant evidence for interaction between carbonate-rich melts, including diamondiferous kimberlites, and mantle wall rocks en route to surface, the effects of this interaction on melt compositions are poorly constrained. Here, we demonstrate a robust linear correlation between the Mg/Si ratios of kimberlites and their entrained mantle components and between Mg/Fe ratios of mantle-derived olivine cores and magmatic olivine rims in kimberlites worldwide. Combined with numerical modeling, these findings indicate that kimberlite melts with highly variable composition were broadly similar before lithosphere assimilation. This implies that kimberlites worldwide originated by partial melting of compositionally similar convective mantle sources under comparable physical conditions. We conclude that mantle assimilation markedly alters the major element composition of carbonate-rich melts and is a major process in the evolution of mantle-derived magmas.

Silicate Melt Inclusions in Diamonds of Eclogite Paragenesis from Placers on the Northeastern Siberian Craton

New findings of silicate-melt inclusions in two alluvial diamonds (from the Kholomolokh placer, northeastern Siberian Platform) are reported. Both diamonds exhibit a high degree of N aggregation state (60–70% B) suggesting their long residence in the mantle. Raman spectral analysis revealed that the composite inclusions consist of clinopyroxene and silicate glass. Hopper crystals of clinopyroxene were observed using scanning electron microscopy and energy-dispersive spectroscopic analyses; these are different in composition from the omphacite inclusions that co-exist in the same diamonds. The glasses in these inclusions contain relatively high SiO2, Al2O3, Na2O and, K2O. These composite inclusions are primary melt that partially crystallised at the cooling stage. Hopper crystals of clinopyroxene imply rapid cooling rates, likely related to the uplift of crystals in the kimberlite melt. The reconstructed composition of such primary melts suggests that they were formed as the product of metasomatised mantle. One of the most likely source of melts/fluids metasomatising the mantle could be a subducted slab.

Djerfisherite in monticellite rocks of the Krestovskaya Intrusion (Polar Siberia)

Djerfisherite in the monticellite rocks of the Krestovskaya Intrusion is found in primary melt inclusions, mono- and polysulfide globules, and in the djerfisherite–hydrogarnet segregations. Melt inclusions are represented by three types. Type I is observed in the cores of perovskite phenocrysts and monticellite grains and corresponds to one of the early crystallization stages of the parental larnite-normative alkali ultrabasic magma enriched in water and other volatiles. Daughter phases of the inclusions are clinopyroxene, serpentine, phlogopite, apatite, nepheline, hydrogarnet, magnetite, djerfisherite, pectolite, and calcite. In some type I inclusions, melt at 1230–1250°C was immiscibly split into two fractions: alkali silicate fraction and highly fluidized water-bearing low-silica fraction enriched in alkali, sulfur, and CO2. The types II and III inclusions in perovskite, monticellite, Ti-garnet, and melilite were formed through the spatial separation of immiscible phases. This follows from the similarity of the modal composition of types II and III melt inclusions to the normative composition of immiscible fractions of type I inclusions. Type II inclusions contain mainly water-bearing silicate daughter phases (hydrogarnet, serpentine, phlogopite, and pectolite), as well as djerfisherite, calcite, and magnetite, Type III inclusions contain clinopyroxene, nepheline, apatite, magnetite, djerfisherite, calcite, and pectolite. The djerfisherite–hydrogarnet segregations are confined to the Ti-magnetite and perovskite phenocrysts and fractures radiating from them in monticellite. The mineral composition of the djerfisherite–hydrogarnet segregations together with their surrounding is similar to the composition of type II inclusions containing similar water-bearing silicates, djerfisherite, calcite, and magnetite. Such similarity gives grounds to relate the formation of the djerfisherite–hydrogarnet segregations, as type II inclusions, with the spatial separation and crystallization of highly fluidized low-silica melt enriched in water, alkalis, sulfur, and CO2. According to the homogenization experiment, the crystallization of highly fluidized melt at 990–1090°C was accompanied by silicate–sulfide immiscibility and the formation of globular, emulsion-like, and myrmekite structures in the djerfisherite–hydrogarnet segregations, as well as mono- and polysulfide globules with djerfisherite in the hydrogarnet–calcite–serpentine substrate. The formation of ferrobrucite–carbonate–hydrogarnet globules in the djerfisherite–hydrogarnet segregations was also related to melt liquation, which again confirms the magmatic origin of the latter. Sometimes, djerfisherite in the djerfisherite–hydrogarnet segregations becomes coarser and forms rims, bands, and veinlets, which is likely explained by the high mobility and low viscosity of sulfide melt. Scarce grains of heazlewoodite, godlevskite, and pentlandite hosted in the djerfisherite–hydrogarnet segregations frequently have the same shape as djerfisherite, which indirectly suggests their simultaneous crystallization from the same melt. The chemical composition of the djerfisherite from mono- and polysulfide globules, djerfisherite–hydrogarnet segregations, and type I inclusions, as most Yakutian kimberlites, is characterized by the high (12.1–16.7 wt %) Ni and low (0.1–0.9 wt %) Cu contents. The composition of the djerfisherite from types II and III inclusions differs in the lowered (3.3–1.6 wt %) Ni and elevated (40.9–53.2 wt %) Fe contents; type III inclusions have high Cu content: from 7.6 to 10.6 wt %.