Diopside Melt Research Articles

Elastic wave velocity measurements of sodium aluminosilicate glass and melt at high pressure and temperature

The combination of ultrasonic technique with synchrotron X-ray diffraction and radiography in a multi-anvil apparatus was utilized to measure the elastic wave velocities of sodium aluminosilicate glass and melt with the partially depolymerized composition of Na3AlSi3O9 (NAS). The measurements were conducted at pressure and temperature of up to 7.3 GPa and at ambient temperature for glass and up to 4.3 GPa and 2120 K for melt, respectively. The compressional wave velocity (VP) of the NAS glass remained mostly constant up to 4 GPa; subsequently, it increased with increasing pressure. Additionally, the NAS glass exhibited a minimum shear wave velocity (VS) at 4–5 GPa. Alternatively, the VP of the NAS melt was smaller than that of the NAS glass, showing a velocity minimum at ∼2 GPa. The negative pressure dependence of VP of the NAS melt is completely different from the depolymerized diopside (Di) melt, which shows a monotonic increase in VP with pressure. The contrasting behavior of the NAS and Di melts is caused by the difference in their structure, characterized by their degree of polymerization. Natural magma found in the interior of the Earth, such as basalt, has a partially depolymerized composition. This study indicates that the magma can exhibit elastic properties with negative pressure dependence, similar to the NAS melt.

Experimental Investigation of Diopside Melt Viscosity at High Pressure

This paper presents the experimental evaluation of viscosity of the diopside-based model composition conducted at high P-T parameters (at the pressure of 4 GPa and in the temperature range of 1750°C - 1800°C) in the presence of olivine crystals. The experiments are carried out using the multi-anvil high-pressure apparatus of the “split-sphere” type (Russian acronym — BARS) according to the falling sphere method. The traveling time of a platinum (Pt) sphere in a melt is one of the parameters measured in experiments. Measurement of this parameter starts when the given P-T values are attained and stops when the electric current is turned off. There are three main positions of the Pt sphere observed in the experiments. Viscosity is calculated using the Stokes’ Law. It is found out that the Pt sphere velocity decreases expectedly as the relative viscosity of such heterogeneous compositions (liquid + solid phase) increases (in contrast to homogeneous melts). Viscosity values remain low when there is up to 7-10 wt-% of solid phase crystals in magma. The increase of olivine xenocrysts in magma leads to the progressive increase of viscosity values of the melt: by 1.5-2 orders of magnitude at 20-25 wt-%, by 3-3.5 orders of magnitude at 35-40 wt-%. The obtained experimental results allow concluding that the amount of solid phase in magma should be sufficiently low (less than 20-30 wt-%), otherwise, melts of the investigated composition can be moved only by explosive processes.

Nucleation delay in the anorthite-diopside binary system: Models and experiments

Nucleation delay was calculated for crystallization of anorthite (CaAl2Si2O8) and diopside (CaMgSi2O6) from melt, and for crystallization in 3 melts in the anorthite-diopside system using classical nucleation theory and values for equilibrium and transport properties from the literature. Calculations were compared to experiments in the literature and new experiments performed on diopside. Only one value, the activation energy of transport for diopside melt, was adjusted to fit the experiments. The activation energies, interfacial energies, and size of the structural unit of growth used for the end-member compositions were applied to calculate nucleation delays for three mixtures inside the binary. The calculated and experimental nucleation delays were within ~10x of each other, substantiating the use of classical nucleation theory to calculate nucleation delays in this system. Differences between measurements and calculations are probably due to uncertainties in equilibrium and transport properties of the system, particularly the activation energy for transport.

Lutetium incorporation in magmas at depth: Changes in melt local environment and the influence on partitioning behaviour

The structure of two Lu doped (4000 ppm) model end member silicate liquids, a highly polymerised haplogranite (Si–Al–Na–K–O) and a less polymerised anorthite–diopside (Si–Al–Mg–Ca–O), have been studied up to 8 GPa using in situ x-ray diffraction techniques. The results are the first to identify trace rare Earth element incorporation in silicate melts at high pressure. At pressures below 5 GPa, the bonding environment of Lu–O was found to be dependent on composition with coordination number CNLu–O=8 and bond distance rLu–O=2.36 Å in the haplogranite melt, decreasing to CNLu–O=6 and rLu–O=2.29 Å in the anorthite–diopside melt. This compositional variance in coordination number at low pressure is consistent with observations made for Y–O in glasses at ambient conditions and is coincident with a dramatic increase in the partition coefficients previously observed for rare Earth elements with increasing melt polymerisation. With increasing pressure we find that CNLu–O and rLu–O remain constant in the haplogranite melt. However, an abrupt change in both Lu–O coordination and bond distance is observed at 5 GPa in the anorthite–diopside melt, with CNLu–O increasing from 6 to 8-fold and rLu–O from 2.29 to 2.39 Å. This occurs over a similar pressure range where a change in the P-dependence in the reported rare Earth element partition coefficients is observed for garnet–, clinopyroxene–, and olivine–melt systems. This work shows that standard models for predicting trace elements at depth must incorporate the effect of pressure-induced structural transformations in the melt in order to realistically predict partitioning behaviour.

Use of a pressless multianvil high-pressure split-sphere apparatus to measure the silicate melt viscosity

The possibility of using a pressless multianvil high-pressure split-sphere apparatus to measure the viscosity of silicate melts was studied experimentally using as an example diopside melt (CaMgSi2O6) at a pressure of 4.0 GPa and a temperature of 1800°C. The viscosity was calculated by the Stokes formula. The measurement error of the melt viscosity was estimated by the falling ball method. Prospects for using devices of this type to estimate the viscosity of silicate melts at high pressures and temperatures are shown.

Relaxation and Glass Transition in an Isostatically Compressed Diopside Glass

Relaxation of isostatically compressed CaMgSi2O6 (diopside) glass is explored by ex situ differential scanning calorimetric (DSC) experiments. A diopside melt was compressed above its glass transition temperature under isostatic conditions at a pressure of 500 MPa. DSC analysis was performed at ambient pressure after slowly cooling the compressed melt under pressure (i.e., after freezing‐in the densified state). Compression‐induced enhancement of the overshoot in heat capacity was observed in the glass transition region. This indicates that a densified, quenched glass possesses a lower apparent fictive temperature, TfA, than a glass that was cooled under ambient pressure at the same cooling rate. However, a thermodynamic analysis indicates that the fictive temperature produced under pressure, Tf0, is actually much higher than that determined from DSC experiments at ambient pressure (Tf0>TfA).

Mise en évidence d'un mécanisme de carbonatation secondaire dans le manteau supérieur du Languedoc

Lherzolite xenoliths with calcite-rich microgranular secondary aggregates (0.1–1 mm) have been sampled in a Messinian breccia pipe from the northeastern part of the Languedoc volcanic province (South France). Their study shows that the carbonate crystallized at low pressure from a silico-carbonated melt resulting from partial melting of diopside and spinel at depth. This melting has been induced by injection, shortly before the eruption, of CO 2 and H 2O-rich fluids, stored probably within the upper lithospheric mantle and reset in motion by the magma ascension. These fluids would derive from decarbonation of levels of deeper lithospheric mantle previously metasomatized by carbonatitic melts. To cite this article: J.-M. Dautria et al., C. R. Geoscience 338 (2006).

Experimental determination of argon solubility in silicate melts: An assessment of the effects of liquid composition and temperature

The argon solubility of 38 liquids in the system Na 2O-CaO-MgO-Al 2O 3-SiO 2 (NCMAS) has been determined at 1873 K and 1 bar, the argon concentration of presaturated glasses being measured using a static mass spectrometer. For compositions in the subsystem diopside (CaMgSi 2O 6), nepheline (NaAlSiO 4), albite (NaAlSi 3O 8), anorthite (CaAl 2Si 2O 8), argon solubility is generally a linear function of the relative proportion of each end member, solubility being lowest in diopside melt (1.53 10 −5 cm 3 STP · g −1 · bar −1) and highest in albite melt (2.88 10 −4 cm 3 STP · g −1 · bar −1). For the tectosilicate joins studied (SiO 2-Na 2Al 2O 4, SiO 2-CaAl 2O 4, SiO 2-MgAl 2O 4) solubility decreases with decreasing silica content in all cases, being highest for Na-bearing liquids and lowest for Mg-bearing liquids at constant molar silica content. Where comparison is possible our results are in good agreement with data from the literature. When our data are considered in isolation we find that argon solubility shows an excellent correlation with calculated ionic porosity. The covariation of argon solubility and liquid density is also reasonable, that with molar volume less convincing and that with polymerization state (as defined by the ratio of the number of nonbridging oxygens and tetrahedral network forming cations; NBO/T) nonexistent. However, when our data are combined with those from the literature no well constrained correlation between argon solubility and ionic porosity is apparent. Based upon this observation and consideration of the temperature dependence of noble gas solubility it is concluded that ionic porosity is not a universally applicable parameter which may be used to predict noble gas solubility as a function of composition, temperature and pressure. Two new models for calculating argon solubility are proposed, both employing the notion of partial molar argon solubilities. The first uses oxide components, for which partial molar argon solubility is directly proportional to partial molar ionic porosity calculated at 1873 K, irrespective of the temperature of experimental equilibration. The second model, which offers the best fit to the available data, employs tetrahedral units rather than oxides as the proposed melt components. This latter model successfully accounts for reported argon solubilities in simple Al-free systems, in simple Al-bearing systems and in natural liquids. This is interpreted to infer that argon is incorporated in large sites in the liquid structure (such as the space within rings of n-tetrahedra) although further work is required to understand the quantitative links between melt structure and noble gas solubility.

Kinetics and mechanisms of crystal growth and diffusion in a glass-forming liquid

Extensive data on the viscosity, covering 15 orders of magnitude, and crystal growth rate, covering seven orders of magnitude, of liquid diopside (CaO.MgO.2SiO(2)) were collected in a wide range of undercoolings from 1.10T(g) to 0.99T(m) (T(g) is the glass transition temperature and T(m) the melting point). The raw growth rate data were corrected for the increased interfacial temperature produced by the heat released during crystallization. A detailed analysis confirms that growth mediated by screw dislocations reasonably explain the experimental data in these wide ranges of temperatures and growth rates. Effective diffusion coefficients were calculated from crystal growth rates and from viscosity, and were then compared with measured self-diffusion coefficients of silicon and oxygen in diopside melt. The results show that oxygen and silicon control the diffusion dynamics involved in crystal growth and viscous flow. This study not only unveils the transport mechanism in this complex liquid, but also validates the use of viscosity (through the Stokes-Einstein or the Eyring equations) to account for the kinetic term of the crystal growth expression in a wide range of temperatures.

An equation of state for silicate melts. III. Analysis of stoichiometric liquids at elevated pressure: shock compression data, molecular dynamics simulations and mineral fusion curves

Experimental data and molecular dynamics simulations that constrain the densities of liquids of “mineral-like” stoichiometry at elevated pressure are evaluated using the liquid Equation of State (EOS) of Ghiorso (2004a). Phase equilibrium constraints on melt density are developed from experimental brackets on mineral fusion curves, specifically congruent melting of albite, anorthite, cristobalite/quartz/stishovite, diopside, enstatite, fayalite, forsterite, jadeite, nepheline, pyrope, sanidine, and titanite. A self consistent thermodynamic analysis of shock compression is applied to experimentally determined brackets on the Hugoniot for the liquid compositions CaMgSi₂O₆, CaAl₂Si₂O₈, Fe₂SiO₄, and (CaMgSi₂O₆)_0.64(CaAl₂Si₂O₈)_0.36. Molecular dynamics (MD) simulations of both melt density and melt structure are analyzed utilizing the liquid EOS of Ghiorso (2004a) and an ideal associated solution model that accounts explicitly for the effect of pressure and temperature on the oxygen coordination environment of silicon and aluminum. MD data on Mg₂Si₂O₆, CaMgSi₂O₆, SiO₂, Na₂Si₄O₉, CaAl₂Si₂O₈, NaAlSiO₄, NaAlSi₂O₆, and NaAlSi₃O₈ liquids are considered in conjunction with the fusion curve and shock compression experimental data sets. An internally consistent assessment of liquid EOS parameters from all available data sources is attempted for each liquid composition considered. Shock compression experiments on more chemically complex liquids of komatiite and MORB bulk composition are also examined. In support of the analysis of mineral fusion curves, volumetric properties as a function of temperature and pressure of diopside, enstatite (both <i>Pbca</i> and <i>C2/c</i>), fayalite, forsterite, and pyrope are evaluated from literature data. Experimental observations are parameterized to a Universal EOS (Vinet and others, 1986, 1987, 1989). It is found that the reference pressure properties derived by Ghiorso and Kress (2004) are internally consistent with the majority of high-pressure constraints on melt density. The notable exceptions are molten SiO₂ and melts in the system MgO-SiO₂. For the latter system, the calibration of Ghiorso and Kress (2004) fails to recover reference pressure volumes. The effect of configurational collapse (the volumetric response associated with changes in melt structure, such as changing oxygen coordination number about a cation) is systematically assessed from molecular dynamics simulation data. Fully depolymerized melts exhibit an ∼11 percent density increase associated with Si and Al transforming from IV- to V-fold coordination with respect to oxygen. Alkali aluminosilicate melts demonstrate ∼27 percent increase in melt density and SiO₂ and Na₂Si₄O₉ liquids show a density increase of ∼17 percent.

Reply to: Comment on: Supercooled diopside melt: confirmation of temperature-dependent expansivity using container-based dilatometry by J. Gottsmann and D.B. Dingwell

Reply to: Comment on: Supercooled diopside melt: confirmation of temperature-dependent expansivity using container-based dilatometry by J. Gottsmann and D.B. Dingwell

Comment on: Supercooled diopside melt: confirmation of temperature-dependent expansivity container-based dilatometry by J. Gottsman and D.B. Dingwell

Comment on: Supercooled diopside melt: confirmation of temperature-dependent expansivity container-based dilatometry by J. Gottsman and D.B. Dingwell

Supercooled diopside melt: confirmation of temperature-dependent expansivity using container-based dilatometry

The expansivity of supercooled diopside liquid has been determined using techniques of container-based dilatometry. Two thermal strategies have been employed, one in which the sample is brought to volumetric equilibrium by long-duration dwells at low temperatures (817 °C) and one in which scanning dilatometry of the sample has been performed at somewhat higher temperatures (890–913 °C). The results of both experiments yield a supercooled liquid expansivity for diopside liquid in the temperature range of 817–913 °C of 84.4 ± 2.8 × 10−4 cm3/mol K. The expansivity is 65% higher than that obtained for diopside melt obtained at superliquidus temperatures using the double bob Archimedean method. Combined fitting of the new low temperature, volume–temperature data from the present study and the superliquidus data from the literature has been performed. The combined fit yields the following equations for the volume–temperature relationship of diopside liquid (T=temperature in °C): $$$$ $$$$

Structure and dynamics of magnesium in silicate melts; a high-temperature25Mg NMR study

25 Mg NMR spectra for several silicate and aluminosilicate melts were obtained from 1000-1470 °C. The peaks are initially very broad, but narrow with increasing temperature to near 500 Hz at the highest temperatures. The peak positions for most of the melts do not shift noticeably with temperature in the range studied, except for a sodium magnesium silicate composition that was previously studied by Fiske and Stebbins (1994). This material showed a decrease in frequency of the peak position by about 4 ppm between 1150-1360 °C in both this and the previous study, consistent with an increase in the average size of the site. The chemical shifts vary with composition as well, ranging from 31 ppm for a potassium sodium magnesium silicate melt to 22 ppm for diopside melt (CaMgSi 2 O 6 ) at 1400 °C. Compositions with higher field strength cations have lower frequency chemical shifts, which correspond to larger coordination numbers and bond lengths for Mg 2+ . All of the peak positions obtained fall to slightly higher frequency than the range for sixfoldcoordinated Mg in crystals and well below the fourfold-coordinated range, indicating that the Mg is in fivefold to sixfold coordination in the melts. Spin-lattice relaxation times show that measurements are on the high-temperature side of the T 1 minima, and a simple expression for quadrupolar relaxation can be used to obtain correlation times for the motion responsible for the relaxation. The correlation times obtained in this manner are very similar to the correlation time τ shear obtained from viscosity measurements, implying that the Mg motion is strongly coupled to the network motion at these temperatures. Line widths also scale with T 1 in this temperature range, leading to the conclusion that the viscosity is the fundamental limit to observing the 25 Mg signal in the melt.

Trace element diffusion in jadeite and diopside melts at high pressures and its geochemical implication

Diffusivities of geochemically important trace elements (eleven rare earth elements (REE), Rb, Sr, Ba, and Y) in jadeite and diopside melts and those of Zr, Nb, Th, and U in jadeite melt have been measured at pressures between 7.5 and 20 kbar and at temperatures 50–200° above the liquidus, using diffusion couples and ion microprobe analysis. The concentrations of these elements in the experimental charges are close to those in natural igneous rocks. In the jadeite melt which is nearly fully polymerized (NBO/T ∼ 0), (1) diffusivities of REE increase with increasing ionic radii, (2) diffusivities of tri- and tetravalent elements increase with increasing pressure at constant temperature, whereas those of mono- and divalent elements do not change significantly with pressure, and (3) diffusivities of these elements decrease with increasing their ionic charge at constant pressure and temperature. In the diopside melt which is considerably less polymerized (NBO/T ∼ 2), (1) diffusivities of these trace elements depend mainly on their ionic radii rather than ionic charges; the diffusivities of mono- and divalent ions decrease with increasing ionic radii at constant pressure and temperature, and (2) diffusivities of REE are nearly the same as that of Ca and decrease with increasing pressure at constant temperature. The behavior of these trace elements is correlated with that of major elements; in the jadeite melt, tri- and tetravalent elements behave similarly to network-forming cations Al and Si, whereas mono- and divalent elements behave as network-modifying cations similarly to Na. In the diopside melt, the diffusion behavior of all these trace elements is similar to that of network-modifying cations Ca and Mg. The results of the present experiments suggest that the abundance of some trace elements in igneous rocks may have been affected by diffusion process at the magmatic stage. In the case of REE, for example, if two different magmas with high and low REE concentrations become in contact one another by multiple intrusion, and a zoned magma chamber is formed, diffusion begins to take place between them, and near the interface, the REE-enriched magma will become more light REE-depleted, whereas REE-depleted magma will become more light REE-enriched, and in addition, if magmas are reduced, the former will show a negative Eu anomaly, whereas the latter will show a positive Eu anomaly.

Diffusivities of Rare Earth Elements and Ba in Magmatic Silicate Melts at High Pressures.

Diffusivities of 11 rare earth elements (REE) and Ba in jadeite (NaAlSi2O6) and diopside (CaMgSi2O6) melts have been measured at pressures between 10 and 20kbar. In jadeite melt, diffusivities of REE increase regularly with increasing their ionic radii, light REE (e.g., La and Ce) diffuse faster than heavy REE (e.g., Yb and Lu) by about 30%, Eu diffuses faster by factor of 8 to 12 than other REE under reducing conditions, and diffusivities of REE increase with increasing pressure at constant temperature. In diopside melt, diffusivities of REE are nearly the same as that of Ca and decrease with increasing pressure. The present study demonstrates that diffusion process in magma should change the relative abundances of REE and also generate Eu anomalies without involvement of plagioclase feldspar. This diffusion-induced process is a newly recognized mechanism of changing the relative REE abundances in magmas and generating Eu anomalies, and it must be taken into account in interpreting the REE abundance patterns of igneous rocks.

Melting experiments on the enstatite-diopside join at 70-224 kbar, including the melting of diopside

Melting relations on the enstatite−diopside (En, Mg2Si2O6−Di, CaMgSi2O6) join, including the compositions of crystalline phases and melts coexisting along the solidi, were experimentally determined in the pressure range 70–224 kbar with a split-sphere anvil apparatus (USSA-2000). Melting is peritectic in enstatite-rich compositions at 70–124 kbar (1840–2100° C) and eutectic at higher pressures, while the diopside-rich clinopyroxene melts azeotropically at 70–165 kbar and up to 300° C lower temperatures than the eutectic. Orthopyroxene is replaced with enstatite-rich clinopyroxene at 120 kbar and 2090°C. First garnet with 17 mol% Di forms on the solidus at 158 kbar and 2100° C. Two garnets coexist on the solidus at 165–183 kbar and 2100° C, garnet coexists with CaSiO3 perovskite at 183–224 kbar (2100–2230° C) and two coexisting perovskites are stable at higher pressures. The melting curve of diopside was determined at 80–170 kbar; the slope becomes negative at 140 kbar and 2155° C. At 170 kbar and 2100° C, diopside with 96% Di breaks down to garnet with 89% Di and CaSiO3 perovskite. The new data were used to calculate an improved temperature-pressure phase diagram for the CMAS system, which can be useful for estimating the mineralogy of the Earth's upper mantle.

Universal viscosity-equation for silicate melts over wide temperature and pressure ranges

The viscous behavior of melts in the system diopside-anorthite has been studied to find a universal viscosity-equation independent of pressure and composition. The present results suggest that the WLF-equation is appropriate: all viscosity-temperature data of six melts along the diopsideanorthite join over a wide temperature range at 0.1 MPa pressure are plotted on a unified curve in accordance with the WLF-equation. For diopside melts, the equation also works well at high pressures up to 2 GPa; it includes the success of estimation of pressure dependence of the glass-transition temperature ( T g), d T g/d P, using viscosity data both at 0.1 MPa and high pressures. If one has only three constants; T g at 0.1 MPa, the viscosity at T g and the d T/ gd P value, it is possible to estimate not only the viscosity-temperature relation but also the pressure dependence for these melts. The configurational entropy theory provides a theoretical background for the WLF-equation in interpreting aspects of the viscous behavior of these melts.

Early partial melting of diopside under high pressure

Early partial melting (EPM) in pyroxenes begins by the precipitation of tiny droplets (0.1 μm or less) of a molten phase highly enriched in silica. At room pressure, EPM starts at temperatures markedly lower than the pyroxene solidus temperatures approximately (250°C below). High-pressure, high-temperature experiments (up to 1.9 GPa and 1309°C) were carried out in a piston-cylinder apparatus on diopside single crystal bearing 1.2 wt.% FeO, to determine the influence of pressure on this phenomenon. The systematic transmission electron microscopy investigation of the samples annealed at high- T, high- P reveals that EPM occurs up to P ≈ 1.5 GPa above 1208°C, at pO 2 ranging from 2.0 × 10 −17 and 2.5 × 10 −16 MPa. These T-P conditions are well below the solidus temperature of pure CaMgSi 2O 6 (1594°C at 1.5 GPa). For pressures above 1.7 ± 0.2 GPa, no EPM precipitates are found in sample annealed for 2 h 30 min at temperatures up to 1309°C.

Viscosity-temperature relationships at 1 atm in the system nepheline-diopside

The viscosities of melts at 1 atm in the system nepheline-diopside have been measured using rotational and beam-bending techniques. At high temperature, melt viscosities decrease with increasing diopside component. This decrease in melt viscosity can be attributed to a reduction in the size of the flow units resulting from an increase in the number of nonbridging oxygens per tetrahedron. The low-temperature viscosity minimum at intermediate compositions develops as a consequence of the different viscosity-temperature profiles of nepheline and diopside melts.