Saturated Melt Research Articles

Clinopyroxene dissolution in basaltic melt

The history of magmatic systems may be inferred from reactions between mantle xenoliths and host basalt if the thermodynamics and kinetics of the reactions are quantified. To study diffusive and convective clinopyroxene dissolution in silicate melts, diffusive clinopyroxene dissolution experiments were conducted at 0.47–1.90 GPa and 1509–1790 K in a piston-cylinder apparatus. Clinopyroxene saturation is found to be roughly determined by MgO and CaO content. The effective binary diffusivities, D MgO and D CaO, and the interface melt saturation condition, C 0 MgO × C 0 CaO , are extracted from the experiments. D MgO and D CaO show Arrhenian dependence on temperature. The pressure dependence is small and not resolved within 0.47–1.90 GPa. C 0 MgO × C 0 CaO in the interface melt increases with increasing temperature, but decreases with increasing pressure. Convective clinopyroxene dissolution, where the convection is driven by the density difference between the crystal and melt, is modeled using the diffusivities and interface melt saturation condition. Previous studies showed that the convective dissolution rate depends on the thermodynamics, kinetics and fluid dynamics of the system. Comparing our results for clinopyroxene dissolution to results from a previous study on convective olivine dissolution shows that the kinetic and fluid dynamic aspects of the two minerals are quite similar. However, the thermodynamics of clinopyroxene dissolution depends more strongly on the degree of superheating and composition of the host melt than that of olivine dissolution. The models for clinopyroxene and olivine dissolution are tested against literature experiments on mineral–melt interaction. They are then applied to previously proposed reactions between Hawaii basalts and mantle minerals, mid-ocean ridge basalts and mantle minerals, and xenoliths digestion in a basalt at Kuandian, Northeast China.

Interphase tension at the boundary of stratifying lithium fluoride-cesium halide melts

Interphase tension at the boundary between mutually saturated melts of the stable diagonal of lithium fluoride-cesium halide reciprocal systems was measured by the meniscus weight method. The roles played by the temperature and halide anion size in the behavior of the interphase layer are discussed. The criticality type of liquid-liquid phase transitions in ionic melts was established.

Distribution of groups I and II elements between liquidus phases of fluorine-saturated Si-Al-Na-K-Li-H-O system

Experimental data allow modeling the behavior of the named elements during formation of fluorine- saturated leucocratic rocks of silicic and alkaline compositions. The distribution of alkaline and alkaliearth elements is discussed at equilibrium between the silica-alumina melt with fluoride phases (crystalline and liquid) and with feldspar. Cryolite crystals form during saturation of silica-alumina melt of normal alkalinity with fluorine. Continuous solid solution of sodium-potassium cryolite is stable at 800°C. The equilibrium between melt and crystals continues up to the maximum molar fraction of 0.1 lithium end member in cryolite, at which two fluoride phases (crystalline and liquid) coexist with the silica-alumina melt of fixed composition. Separation of salt melts during late differentiation stages of granite and alkaline rocks is a regular process continuing the natural evolution of ore-magmatic systems. At equilibrium of two liquid phases, the silica phase is relatively enriched in potassium, and the fluoride phase is substantially enriched in sodium. This detected effect is the only currently possible mechanism for the occurrence of the potassium differentiation trends of granite melts. All effects related to crystallization cause enrichment in sodium. In other cases (with Ca, Sr, Mg, Rb, and Cs), separation of the second liquid phase acts in the same direction and enhances the action of crystallization. Comparison between partition coefficients allows derivation of the following affinity rows of alkaline elements for fluoride melt: Li > Na > K > Rb≈Cs and Mg > Ca > Sr > Ba. Hence, the known rule for joining strong bases with strong acids and weak bases with weak acids is fulfilled.

Structure of KTiOPO4 single crystals grown by the top-seeded solution and spontaneous flux crystallization methods

This paper reports on the results of precision X-ray structural investigations of KTiOPO4 single crystals grown by one method (crystallization from a solution in the melt) in two variants (the spontaneous formation of crystallization centers or top-seeded solution growth during slow cooling of saturated solution melts). It is shown that spontaneous flux crystallization leads to the formation of a larger number of defects. Potassium atoms are found to be disordered. The splitting of the K1 and K2 potassium positions is equal to 0.347(4) and 0.279(3) A, respectively, for the crystals grown by the top-seeded solution method and 0.308(5) and 0.321(4) A, respectively, for the crystals grown through the spontaneous flux crystallization.

Experimental investigation of K and Na partitioning between miscible liquids

Model silicate melts with variable Al2O3 and SiO2 contents were experimentally saturated with alkalis at a total pressure of 1 atm and temperatures of 1300–1470°C, using the crucible supported loop technique. It was shown that Al2O3 content has little influence on the degree of silicate melt saturation with K and Na. In contrast, SiO2 content strongly affects the solubility of alkalis in silicate melts. Model calculations were performed to evaluate the behavior of alkalis during the contamination/mixing of basic and silicic magmas.

Geochemistry of ultra-potassic rhyodacite magmas from the area of the Orlovka Massif of Li-F granites in Eastern Transbaikalia: Evidence from study of melt inclusions in quartz

Dikes, stocks and/or sheet flows of felsic volcanic and subvolcanic rocks are typically observed in the vicinity of rare-metal Li-F granite massifs. Their ubiquitous spatial association to rare-metal granites and, often, geochemical affinity to them suggest their certain petrological relation. Compositionally unique ultrapotassic trachydacites enriched in many rare elements were found among these rocks within the Khangilay complex of ore deposits in Eastern Transbaikalia. Melt inclusions in rock-forming quartz were studied to reconstruct the composition and evolution of parent melt. The obtained data demonstrated the existence of a super-potassic peraluminous melt (K2O = 6.12 wt %, Na2O = 1.08 wt %) having elevated contents of rare lithophile elements (730 ppm Rb2O and 900 ppm BaO). The ion-microprobe content of Li is 354.23 ppm at a relatively low F content (up to 0.5 wt %). The residual melt is characterized by the most unusual composition: extremely low contents of mafic components and basicity (< 0.5 wt % femic oxides), a high Al index (A/CNK = 1.53) at comparatively low SiO2 (60 wt %), and high total sodic alkalinity (more than 10 wt % K2O + Na2O; 6.11 wt % Na2O). Such a composition corresponds to ongonite magma. However, the melt contains no F but has a high Cl content (0.34 wt %), which corresponds to the limit Cl saturation of haplogranite melt. SHRIMP-II U-Pb zircon dating showed significant difference between rare metal granites and trachyrhyodacites of the Khangilay complex of ore deposits: 139.9 ± 1.9 Ma and 253.4 ± 2.4 Ma, respectively. The geochemical similarity of these rocks, primarily in terms of abundance of refractory elements, REE distribution patterns, and initial Sr ratio, indicates their derivation from similar protolith.

Hydrothermal Evolution of the Sonajil Porphyry Copper System, East Azarbaijan Province, Iran: The History of an Uneconomic Deposit

The Sonajil porphyry copper system formed in a small, relatively deep-seated (~5 km) granodioritic intrusion at Ahar, East Azarbaijan, Iran. Based on field geology, petrography and fluid inclusion studies, early hydrothermal alteration caused a potassic-type alteration in the deep, central parts of the intrusion, and generated a peripheral propylitic halo. Dominant phyllic alteration overprinted apical parts of the intrusion. Hypogene copper mineralization was associated with potassic alteration. The earliest fluid circulated in the complex had high salinity (35-60 wt% NaCl equiv.), and is interpreted to have been formed directly from the crystallizing magma. Major entrapment of this fluid, which is responsible for potassic alteration and deposition of chalcopyrite and bornite in thin, discontinuous Group I and II veins, occurred after cooling to about 400°C. The average Cu grade in the potassic alteration zone is between 0.01 and 0.07%. Circulation of a lower temperature fluid having a homogenization temperature of 220-350°C with meteoric H2O that originated in the peripheral parts of the system was responsible for propylitic alteration. During an intermediate phase of hydrothermal activity, meteoric water penetrated central parts of the system along a network of late fractures (Group III veins) and is partly responsible for the Group II veins. Mixing of the later fluid with the magma-derived high-salinity fluid created a fluid characterized by salinities ranging from 1 to 25 wt% NaCl equiv. The inflow of meteoric water, and a continuous temperature decrease within the system, produced more oxidized fluids, which caused phyllic alteration and intense copper leaching. Late boiling in the apical parts of the system favored deposition of sporadic chalcopyrite and bornite, but did not add significant copper. Supergene enrichment led to copper grades higher than that of phyllic zone, but not enough to be of economic significance. Based on the similarities in wall-rock alteration, mineralization style, petrography, and fluid evolution in Sonajil and those of typical productive porphyry copper deposits, the lack of economic mineralization in Sonajil is surprising. It is proposed that this is mainly due to the deep level of emplacement of the intrusion and the dacitic composition of the parental magma. These factors are considered to be the main causes preventing melt saturation with alkali chloride-enriched fluids until the late stage of crystallization, which restricted the amount of exsolved fluid and Cu extracted from the melt. Moreover, overpressuring of the upper parts of the system and a lack of wide apical stockwork veins failed to provide sites for the mineralizing fluids to concentrate copper to economic levels. Finally, the uneconomic nature of the Sonajil porphyry could reflect the lack of multiple intrusions and the intense Cu leaching of the phyllic alteration zone.

Effect of Dissolution on the Ni&lt;sub&gt;3&lt;/sub&gt;Sn&lt;sub&gt;4&lt;/sub&gt; Growth Kinetics at the Interface of Ni and Liquid Sn-Base Solders

The Ni3Sn4 intermetallic layer occurs at the interface of nickel and the saturated or undersaturated Sn-base solder melt at 250-450 °C and dipping times of 300 to 2400 s. Mathematical equations are proposed to evaluate the thickness of the Ni3Sn4 layer formed under conditions of simultaneous dissolution in the undersaturated solder melt.

Solubility of corundum in the system Al 2O 3–SiO 2–H 2O–NaCl at 800 °C and 10 kbar

The solubility of corundum was measured at 800 °C and 10 kbar in NaCl–H 2O–SiO 2 fluids over NaCl mole fractions ( X NaCl) of 0 to 0.5 and SiO 2 concentrations of zero to quartz or albite + melt saturation, depending on X NaCl. Experiments were performed in a piston-cylinder apparatus. Dissolved Al 2O 3 and SiO 2 were determined by weight losses of corundum and quartz crystals, or by bulk compositions of bracketing experiments. Although kyanite and sillimanite are slightly more stable than corundum + quartz at these pressures ( P) and temperatures ( T), neither appeared in any of the experiments. Results indicate that the enhancement of corundum solubility by NaCl at this P and T is further promoted by the addition of SiO 2. At quartz saturation, significant enhancement occurs in initially pure H 2O and addition of NaCl yields yet higher Al 2O 3 concentrations. At 0.03 ≤ X NaCl ≤ 0.1, quartz saturation is replaced by albite + silicate melt. The anhydrous melt composition is nearly on the join NaAlSi 3O 8–SiO 2. Al 2O 3 molality rises rapidly with NaCl concentration to 0.038 at X NaCl = 0.1 and then increases more slowly to 0.052 at halite saturation. There is, in addition, a measurable reciprocal enhancement of Si solubility by virtue of dissolved Al at a fixed X NaCl. Quench pH in NaCl-bearing fluids is strongly acidic and Na/Cl < 1 in quench solutes, suggesting low pH at high P and T. These observations, combined with previous work indicating Si–Al and Na–Al complexing, lead to the hypothesis that the reciprocal solubility enhancement of Al and Si is due to formation of Na-aluminosilicate complexes. Mass balance consideration suggests that the bulk Si/Al ratio of the group of complexes ranges from 1 to 2 in the NaCl-free system, to > 3 at high X NaCl. Our data show that Al 2O 3 is a moderately soluble component in quartz + aluminosilicate-saturated rocks in the presence of intergranular salt solutions at deep-crustal metamorphic P– T conditions and commonly realized salinities. Al 2O 3 should not be regarded as a fixed reference component, because it may exhibit substantial mobility.

Calving and ice-shelf break-up processes investigated by proxy: Antarctic tabular iceberg evolution during northward drift

AbstractUsing a combination of satellite sensors, field measurements and satellite-uplinked in situ observing stations, we examine the evolution of several large icebergs drifting east of the Antarctic Peninsula towards South Georgia Island. Three styles of calving are observed during drift: ‘rift calvings’, ‘edge wasting’ and ‘rapid disintegration’. Rift calvings exploit large pre-existing fractures generated in the shelf environment and can occur at any stage of drift. Edge wasting is calving of the iceberg perimeter by numerous small edge-parallel, sliver-shaped icebergs, preserving the general shape of the main iceberg as it shrinks. This process is observed only in areas north of the sea-ice edge. Rapid disintegration, where numerous small calvings occur in rapid succession, is consistently associated with indications of surface melt saturation (surface lakes, firn-pit ponding). Freeboard measurements by ICESat indicate substantial increases in ice-thinning rates north of the sea-ice edge (from &lt;10 m a−1 to &gt;30 m a−1), but surface densification is shown to be an important correction (&gt;2 m freeboard loss before the firn saturates). Edge wasting of icebergs in ‘warm’ surface water (sea-ice-free, &gt;−1.8°C) implies a mechanism based on waterline erosion. Rapid disintegration (‘Larsen B-style’ break-up) is likely due to the effects of surface or saturated-firn water acting on pre-existing crevasses, or on wave- or tidally induced fractures. Changes in microwave backscatter of iceberg firn as icebergs drift into warmer climate and experience increased surface melt suggest a means of predicting when floating ice plates are evolving towards disintegration.

Investigation of the processes of dissolution and saturation of aluminum melts by iron

The process of dissolution of iron-containing additives in aluminum melts is considered. Based on the data of the investigation of the kinetics and saturation of Al melts by iron, recommendations on the modes of remelting of the aluminum melt polluted with iron are made. The mechanism of formation and growth of the intermetallic layer is suggested.

Solidification of Precirol ® by the expansion of a supercritical fluid saturated melt: From the thermodynamic balance towards the crystallization aspect

The following article presents the thermodynamic and crystallization aspects of the solidification through expansion of a melted fat, Precirol ®, previously saturated with supercritical CO 2. A simplified macroscopic energy balance is used to understand the mixture behaviour during expansion. It allows the quantification of the CO 2 to be added to the mixture in order to control the state and the temperature of the compound at the outlet of the expansion device. The required physico-chemical parameters were determined experimentally. The variation of the operating parameters appearing in the energy balance revealed three regions/areas of possible states for the expanded lipid: solid, molten or solid–liquid equilibrium. This, together with the outlet temperature could be tuned by varying not just the inlet or saturation conditions, but also the ratio of supercritical CO 2 to be expanded with the saturated fat. As for the crystallization aspect, the variation of chemical potential, which is the driving force, was calculated; the critical radius of nuclei and the nucleation rates were estimated according to the classic melt media theory. The main assumptions were that solidification occurred mainly at atmospheric pressure and that only homogeneous nucleation took place. The orders of magnitude obtained put in light the necessity to determine precisely the viscosity of the melt saturated fat and the solid/melt interfacial tension.

Modelling of structural formation in ordered porosity metal materials

A two-dimensional time dependent model for simultaneous growth of gas pore and solid phase from gas saturated melt was developed. This model was applied to structure formation of ordered porosity metal materials. Fabrication of copper porosity castings was simulated numerically. A procedure for calculating inter-pore spacing and pore radius for a certain technological regime was discussed. It was proved that the structure of ordered porosity metal materials formed at steady-state conditions could consist of pores with different radii. This is observed in real ingots. This is the main distinction between normal eutectic structures and ordered porosity structure.

Dunite channels as viable pathways for mare basalt transport in the deep lunar mantle

Lunar picritic glasses are multisaturated with olivine and orthopyroxene at pressures up to 2.45 GPa. This corresponds to a depth of approximately 490 km in the lunar mantle and represents a minimum estimate of the depth of melt generation. Models that propose a mechanism to move these melts through the mantle and crust generally involve the creation of a network of fractures through which melt can rise very rapidly, minimizing its interaction with shallower mantle. We carried out an experimental study of harzburgite dissolution in a synthetic high Ti red glass. Our results show that during ascent of olivine saturated melts, dissolution of wallrock orthopyroxene and precipitation of olivine leads to the formation of high porosity, high permeability dunite channels that efficiently shield subsequent melts from reaction with the mantle. These dunite channels are similar to dunite dikes observed in ophiolite sequences which are believed to be channels for mid‐ocean ridge basalts. Models for lunar melt migration that require brittle fracturing extending to the depths of multisaturation need not be invoked.

Reaction Mechanism between Solid CaO and FeOx–CaO–SiO2–P2O5 Slag at 1 573 K

Solid CaO and FeOx–CaO–SiO2–P2O5 slag were reacted for 2 to 2 400 s at 1 573 K. The interface of CaO and slag were observed and analyzed by SEM/EDS. The CaO–FeO layer was formed beside solid CaO. The thickness of the CaO–FeO layer increased with time. Next to the CaO–FeO layer, 2CaO·SiO2 phase was formed in the melt and high content of FeO was included in the liquid. The activities of FeO and CaO for each phase were evaluated and reaction mechanism between solid CaO and FeOx–CaO–SiO2–P2O5 slag was discussed. The activity of FeO for 2CaO·SiO2 saturated melt is larger than that for the CaO–FeO layer, therefore, Fe2+ diffuses from slag phase to solid CaO. Then the CaO–FeO layer is formed beside solid CaO. The pass of the slag composition change accompanied by CaO dissolution are represented in the phase diagram for the FeOx–CaO–(SiO2+P2O5) pseudo ternary system.

Detailed studies on the origin of nitrogen-related electron traps in dilute GaAsN layers grown by liquid phase epitaxy

Dilute GaAsN layers are grown by liquid phase epitaxy from saturated melts containing polycrystalline GaN as the source of nitrogen. From photoluminescence measurements the nitrogen content in the material is obtained. Low temperature photocurrent and photocapacitance measurements reveal the presence of an electron trap with an ionization energy of 0.65–0.67 eV in the as-grown layers, whose origin is related to interstitial (N–N)As defects. High temperature annealing of the material almost removed the trap and new electron traps at 0.8 and 0.9 eV are produced. It is suggested that during the annealing process the (N–N)As defects, due to their lower energy of formation, are converted to more thermally stable (AsGa–NAs) or (AsN)As defects which might be the source of the new electron traps. High temperature treatment of the growth melt with erbium is found to remove nitrogen from the grown layer with complete annihilation of all the electron traps.

The Effects of Small Amounts of H2O, CO2 and Na2O on the Partial Melting of Spinel Lherzolite in the System CaO–MgO–Al2O3–SiO2 ± H2O ± CO2 ± Na2O at 1·1 GPa

The effects of small amounts of H2O (<4 wt % in the melt) on the multiply saturated partial melting of spinel lherzolite in the system CaO–MgO–Al2O3–SiO2 Na2O CO2 have been determined at 1 1GPa in the piston-cylinder apparatus. Electron microprobe analysis and Fourier transform infrared spectroscopy were used to analyse the experimental products. The effects of H2O are to decrease the melting temperature by 45 C per wt % H2O in the melt, to increase the Al2O3 of the melts, decrease MgO and CaO, and leave SiO2 approximately constant, with melts changing from olivineto quartz-normative. The effects of CO2 are insignificant at zero H2O, but become noticeable as H2O increases, tending to counteract the H2O. The interaction between H2O and CO2 causes the solubility of CO2 at vapour saturation to increase with increasing H2O, for small amounts of H2O. Neglect of the influence of CO2 in some previous studies on the hydrous partial melting of natural peridotite may explain apparent inconsistencies between the results. The effect of small amounts of H2O on multiply saturated melt compositions at 1 1 GPa is similar to that of K2O, i.e. increasing H2O or K2O leads to quartz-normative compositions, but increasing Na2O produces an almost opposite trend, towards nepheline-normative compositions.

Reaction Diffusion in Mo-Si System above the Melting Point of Silicon

The results of direct kinetic measurements and SEM observations on formation of silicide phases in Mo-Si system at temperatures 1400-1700о С are presented in the work. It was shown, that the formation of MoSi2 proceeds by two different mechanisms and accordingly, two types of microstructures are formed: (i) a compact layer (usually with expressed columnar structure) by the reaction diffusion mechanism; and (ii) separated fine grains by crystallization in the volume of saturated Me-Si melt. A model of product formation is offered which allows to calculate the relative contributions of the two mechanisms of disilicide phase formation at various stages of interaction and to estimate the role each of them in the total process.

Interfacial interaction of solid nickel with liquid bismuth and Bi–base alloys

The dissolution process of nickel in liquid bismuth and a 51%Bi–42%Sn–5%In–2%Zn alloy was investigated by the rotating-disc technique at 300 and 350 °C. The solubility values of nickel in bismuth and its alloy were found to be very different, while the dissolution rate constants were rather close. Appropriate diffusion coefficients were estimated. With bismuth as a melt material, the NiBi 3 intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at holding times up to 3600 s. The NiBi phase is found to be missing. A simple mathematical equation is proposed to evaluate the NiBi 3 layer thickness in the case of undersaturated melts. With a 51%Bi–42%Sn–5%In–2%Zn alloy as a melt material, a very thin intermetallic layer of complicated chemical composition occurs at the Ni–alloy interface. With saturated melts, its growth-rate constant is 5.5 × 10 −16 m 2 s −1 at 350 °C, whereas in undersaturated melts, the intermetallic phase does not form at all, if the liquid agitation is sufficiently strong. The rupture strength of the nickel-to-alloy joints is around 25 MPa. Small additions of Sb, Te and Se (2% in total) to the alloy exert a considerable influence on the intermetallic-layer composition, but have minimal impact on its thickness.

Upper crustal podiform chromitite from the northern Oman ophiolite as the stratigraphically shallowest chromitite in ophiolite and its implication for Cr concentration

A new type of podiform chromitite was found at Wadi Hilti in the northern Oman ophiolite. It is within a late-intrusive dunite body, possibly derived from olivine-rich crystal mush, between the sheeted dike complex and upper gabbro. This chromitite forms small (<30 cm in thickness) pods with irregular to lenticular shapes. Neither layering nor graded bedding is observed within the pods. The chromitite is in the upper crust, by far shallower in ophiolite stratigraphy than the other podiform chromitites that have ever been found in the Moho transition zone to the upper mantle. It is distributed along a small felsic to gabbroic melt pool within the dunite body, which was formed by melting of gabbroic blocks captured by the mush. Chromian spinel was precipitated due to mixing of two kinds of melt, a basaltic interstitial melt from the mush and an evolved, possibly felsic, melt formed by the melting of gabbro blocks. The podiform chromitite reported here is strikingly similar in petrography and spinel chemistry to the stratiform chromitite from layered intrusions. The former contains plagioclase and clinopyroxene as matrix silicates instead of olivine as well as includes euhedral and fine spinel with solid mineral inclusions. Chromian spinel of the upper crustal podiform chromitite from Oman has relatively low content of (Cr2O3 + Al2O3), the Cr/(Cr + Al) atomic ratio of around 0.6, and the relatively high TiO2 content ranging from 1 to 3 wt%. We conclude that assimilation of relatively Si-rich materials (crustal rocks or mantle orthopyroxene) by olivine-spinel saturated melts can explain the genesis of any type of chromitite.