Piston-cylinder Apparatus Research Articles

An experimentally calibrated thermobarometric solubility model for titanium in coesite (TitaniC)

Experiments were conducted to quantify the temperature and pressure effects on the solubility of titanium in coesite. Powdered amorphous silica, titania (anatase), zirconia, and water were added to silver capsules and run in the coesite stability field (at 32, 35, and 40 kbar) from 700 to 1050 °C using a piston–cylinder apparatus. Crystallization of coesite, rutile, and zircon from silica-, titania-, and zircon-saturated aqueous fluids was confirmed by Raman spectroscopy. Cathodoluminescence images and electron microprobe measurements showed that coesite crystals are relatively homogenous. The Ti concentrations of coesite crystals are significantly higher than concentrations predicted using the Ti-in-quartz calibration (Wark and Watson in Contrib Mineral Petrol 152:743–754, 2006. https://doi.org/10.1007/s00410-006-0132-1 ; Thomas et al. in Contrib Mineral Petrol 160:743–759, 2010. https://doi.org/10.1007/s00410-010-0505-3 ). Titanium K-edge X-ray absorption near edge structure (XANES) measurements demonstrate that Ti4+ substitutes for Si4+ on fourfold tetrahedral sites in coesite at all conditions studied. A model was calibrated to describe the effects of pressure and temperature on the solubility of titanium in coesite by using a least-squares method to fit Ti concentrations in coesite to the simple expression: $$RT\ln X_{{{\text{TiO}}_{2} }}^{\text{coesite}} = - 55.068 + 0.00195 \times T\;({\text{K}}) - 1.234 \times P\;({\text{kbar}}) + RT\ln a_{{{\text{TiO}}_{2} }}^{\text{rutile}} ,$$ where R is the gas constant 8.3145 × 10−3 kJ/K, P is pressure in kbar, T is temperature in kelvin, $$X_{{{\text{TiO}}_{2} }}^{\text{coesite}}$$ is the mole fraction of TiO2 in coesite, and $$a_{{{\text{TiO}}_{2} }}^{\text{rutile}}$$ is the activity of TiO2 in the system referenced to rutile. Ti-in-coesite solubility can be used as a thermobarometer for natural samples when used in combination with another indicator of temperature or pressure, such as another thermobarometer in a cogenetic mineral (e.g. rutile) or other phase equilibria (e.g. graphite = diamond). Applications of the Ti-in-coesite thermobarometer to samples from the western Alps and Papua New Guinea are presented.

Electrical Conductivity of Fluorite and Fluorine Conduction

Fluorine is a species commonly present in many minerals in the Earth’s interior, with a concentration ranging from a few ppm to more than 10 wt. %. Recent experimental studies on fluorine-bearing silicate minerals have proposed that fluorine might be an important charge carrier for electrical conduction of Earth materials at elevated conditions, but the results are somewhat ambiguous. In this investigation, the electrical conductivity of gem-quality natural single crystal fluorite, a simple bi-elemental (Ca and F) mineral, has been determined at 1 GPa and 200–650 °C in two replication runs, by a Solartron-1260 Impedance/Gain Phase analyzer in an end-loaded piston-cylinder apparatus. The sample composition remained unchanged after the runs. The conductivity data are reproducible between different runs and between heating-cooling cycles of each run. The conductivity (σ) increases with increasing temperature, and can be described by the Arrhenius law, σ = 10^(5.34 ± 0.07)·exp[−(130 ± 1, kJ/mol)/(RT)], where R is the gas constant and T is the temperature. According to the equation, the conductivity reaches ~0.01 S/m at 650 °C. This elevated conductivity is strong evidence that fluorine is important in charge transport. The simple construction of this mineral indicates that the electrical conduction is dominated by fluoride (F−). Therefore, fluorine is potentially an important charge carrier in influencing the electrical property of Fluorine-bearing Earth materials.

Calibration of high-temperature furnace assemblies for experiments between 200 and 600 MPa with end-loaded piston-cylinder apparatuses

Abstract We present pressure calibration results for piston-cylinder –” and 1” high temperature furnace assemblies in the 200-600 MPa range aiming to expand its applicability to simulate upper crustal conditions. The furnace assemblies were made up by crushable MgO, graphite heater, pyrex glass spacer, and NaCl sleeve. Twenty-one experiments were carried out over a range of pressures (200-600 MPa) and temperatures (870-945°C) to determine the liquidus curve of NaCl. The obtained curve slope fits that given by Siewert et al. (1998), but offsets by ~ -55 MPa, implying the need of a constant P upward correction in the 300-600 MPa and ca. 300-400 MPa pressure ranges for the 3/4” and 1” assemblies, respectively. However, if the NaCl melting points (918-920°C) obtained by Bohlen (1984) at 500 MPa are used as reference, no pressure correction is needed. Larger offsets (to -120 MPa) were obtained under pressure conditions around and lower than 300 MPa with the 1” assembly. Our results confirm the applicability of Bristol-type end-loaded piston-cylinders coupled with appropriate furnace assemblies in assessing relatively low-pressure conditions (down to ~ 200 MPa, ~ 7 km depth) found in the Earth’s upper crust, where important magmatic, hydrothermal and metamorphic processes occur.

Pyrometamorphic aureoles of Cretaceous sandstones and shales by Cenozoic basic intrusions, NE Brazil: Petrograhic, textural, chemical and experimental approaches

In this paper, we present the case study of thermal aureoles developed in Cretaceous sedimentary rocks from the Potiguar Basin (NE Brazil) nearby shallow Cenozoic mafic intrusions. The study integrates the field and petrologic study of the metamorphic aureole with experimental work. The pyrometamorphic aureole is discontinuous and less than one hundred meters wide. Along the contact with the intrusions, sandstones, siltstones and shales were transformed into light and dark buchites. The light buchite has acicular clinoenstatite and tridymite, as well as microphenocrysts of sanidine, sekaninaite, and anorthite, within a gray to brown, SiO2- and K2O-rich and Al2O3- and FeO-poor rhyolitic glass. The dark buchite is richer in FeO and Al2O3 and has pyrometamorphic Al-magnetite, hercynite, and Fe-mullite. Buchites derived from shales have a cryptocrystalline to vitreous groundmass and macroscopically resemble tachylites. A series of low-pressure and high-temperature experiments were conducted at 3 kbar and 1000–1200 °C on a piston-cylinder apparatus using sandstone and shale starting materials sandwiched with olivine basalt. The experimental results indicated that melting occurred at approximately 1150 °C, followed by relatively slow cooling until approximately 1000 °C and then by quenching. This multidisciplinary approach suggested that the sedimentary units were submitted to very high temperatures upon contact with the intrusions, and this outcome is corroborated by the mineralogy and textures observed in the natural rocks.

Zircon saturation in terrestrial basaltic melts and its geological implications

Zircon is a widely used accessary mineral, and zircon saturation in silicate melts has many applications in geology. Based on the original model proposed by Watson and Harrison (Earth Planet. Sci. Lett. 64:295–304, 1983), the quantification of the zircon saturation in melts with felsic and intermediate compositions has recently become a major research topic, resulting in some disagreements and different models. Theoretically, the addition of new data, especially regarding the zircon solubility in a basaltic (peralkaline) melt that can provide an upper limit below which zircon is likely to crystallize in igneous rocks, is thus critical to the development of a new, refined model that can be applied to a wide range of compositions and provide a resolution to the ongoing debate. Here, the zircon saturation in a terrestrial basaltic melt was systematically investigated for the first time using a piston-cylinder apparatus across the temperature range of 1050–1350 °C at pressures of 0.5, 1.0 and 1.5 GPa. We combined our new data on mafic melts with data from previous studies on mafic to felsic melts to investigate the factors affecting zircon saturation in basaltic melts. Our results confirm an extremely high zircon saturation in mafic (peralkaline) melts in addition to its strong dependence on the melt composition and temperature and its weak dependence on the pressure and water content. We used all available data that can be used to calculate compositional parameter G [=(3·Al2O3 + SiO2)/(Na2O + K2O + CaO + MgO + FeO), molar ratio] to evaluate fit to a previous model designed to work with more alkaline compositions and proposed a new refined model, given by (with 1σ errors): lnCZr(melt) = (3.313 ± 0.349)–(1.35 ± 0.10)·lnG + (0.0065 ± 0.0003)·T, where CZr(melt) is the Zr concentration in the melt at zircon saturation and T is temperature in °C. Additionally, we reintroduced the previously proposed dominance of the temperature and melt composition on the degree of polymerization and thus the ability of zircon to enter the melt, thereby leading to large differences in the zircon saturation between intermediate-felsic magmas and mafic magmas. Although mantle-derived basaltic magmas have a low Zr concentration, they are capable of dissolving the zircon in surrounding rocks during their ascent. Zircons are generally rare in extrusive or hypabyssal basaltic rocks but can form during the late crystallization stage of plutonic basaltic magmas; thus, zircon crystallization has little impact on the distribution of trace elements in mafic magmas.

The influence of NaCl-H2O fluids on reactions between olivine and plagioclase: An experimental study at 0.8 GPa and 800–900 °C

The lower to middle continental and oceanic crust is dominated by mafic gabbroic rocks, which are variably metamorphosed at amphibolite-granulite facies conditions forming reaction rims or veins containing secondary pyroxenes, amphibole and phlogopite. Metamorphic fluids in the mid-crust are typically NaCl-rich brines. In this study, olivine and plagioclase were reacted with varying amounts of fluid (0–2 wt% added) that had compositions ranging from pure H2O to NaCl solutions (0–2 mol) in a series of experiments using the piston cylinder apparatus at 0.8 GPa and temperatures from 800 to 900 °C. Coronas of clinopyroxene, clinopyroxene + amphibole, and clinopyroxene + phlogopite were formed. The thicknesses of reaction rims, i.e. the relative amount of reaction rim products, increase with the relative amount of fluid present in the system, and are therefore linked to the level of fluid saturation along grain boundaries and interphase boundaries. Samples with no added H2O, show little to no signs of reaction, indicating the necessity for fluids in initiating a reaction between olivine and plagioclase. The concentration of NaCl in the fluid also increases the rates of rim growth. At 900 °C and 2 wt% added fluid, Cl-rich hydrous dacite-trachyte melt compositions formed and are similar to low degree partial melts of oceanic crust. The Cl contents of secondary amphiboles are positively correlated with the FeO and K2O contents of the amphibole. Consumption of fluid during the formation of hydrous rim phases may lead to high Cl within transient fluid filled pores along grain boundaries, which may lead to locally Cl-rich amphiboles.

Experimental study of quartz inclusions in garnet at pressures up to 3.0 GPa: evaluating validity of the quartz-in-garnet inclusion elastic thermobarometer

Garnet crystals with quartz inclusions were hydrothermally crystallized from oxide starting materials in piston–cylinder apparatuses at pressures from 0.5 to 3 GPa and temperatures ranging from 700 to 800 °C to study how entrapment conditions affect remnant pressures of quartz inclusions used for quartz-in-garnet (QuiG) elastic thermobarometry. Systematic changes of the 128, 206 and 464 cm−1 Raman band frequencies of quartz were used to determine pressures of quartz inclusions in garnet using Raman spectroscopy calibrations that describe the P–T dependencies of Raman band shifts for quartz under hydrostatic pressure. Within analytical uncertainties, inclusion pressures calculated for each of the three Raman band frequencies are equivalent, which suggests that non-hydrostatic stress effects caused by elastic anisotropy in quartz are smaller than measurement errors. The experimental quartz inclusions have pressures ranging from − 0.351 to 1.247 GPa that span the range of values observed for quartz inclusions in garnets from natural rocks. Quartz inclusion pressures were used to model P–T conditions at which the inclusions could have been trapped. The accuracy of QuiG thermobarometry was evaluated by considering the differences between pressures measured during experiments and pressures calculated using published equation of state parameters for quartz and garnet. Our experimental results demonstrate that Raman measurements performed at room temperature can be used without corrections to estimate garnet crystallization pressures. Calculated entrapment pressures for quartz inclusions in garnet are less than ~ 10% different from pressures measured during the experiments. Because the method is simple to apply with reasonable accuracy, we expect widespread usage of QuiG thermobarometry to estimate crystallization conditions for garnet-bearing silicic rocks.

Patterns for efficient propulsion during the energy evolution of vortex rings

Compared with steady-jet propulsion, pulsed-jet propulsion can exhibit more efficient by manipulating the unsteady formation of vortex rings in the near wake. That is, energy is much better transferred and used in the form of vortices to generate propulsive force rather than a steady jet. This study is aimed at analyzing the energy evolution of vortex rings and revealing the patterns for efficient propulsion during the energy evolution. Of particular importance to the energy evolution of vortex rings is the pinch-off mechanism, which is owing to the limiting effects of energy and causes that vortex rings cannot grow indefinitely. Canonical vortex rings are generated by using a piston–cylinder apparatus and their time-dependent flow fields are measured using digital particle image velocimetry. During the energy evolution of vortex rings, overpressure and fluid flux at the exit plane are found to significantly contribute to their energy. Moreover, overpressure is the dominant pattern contributing to the energy of vortex rings and has a greater contribution than fluid flux at the early evolution stage, whereas the contribution of overpressure nearly disappears once vortex rings pinch off. By contrast, fluid flux continuously contributes to the energy of vortex rings until they physically separate from the trailing vortices. Based on the hyperbolic LCSs, distinguishable flow patterns are detected to correspond to the energy evolution of vortex ring. The appearance of a newly disconnected LCS in the trailing jet indicates the initial roll-up of a trailing vortex and the onset of pinch-off, which coincides with the end of overpressure contribution to the energy of vortex rings. A LCS barrier behind the vortex rings appears and prevents any fluid flux from entering the vortex rings, thereby indicating the end of pinch-off and corresponding to the end of fluid-flux contribution. Moreover, it is suggested that transferring or using energy by pressure is a more efficient pattern than fluid flux to generate hydrodynamic force, and enlarging the energy contribution to vortices can further enhance propulsive performance.

High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus

In order to address geological processes at great depths, rock deformation should ideally be tested at high pressure (> 0.5 GPa) and high temperature (> 300 °C). However, because of the low stress resolution of current solid-pressure-medium apparatuses, high-resolution measurements are today restricted to low-pressure deformation experiments in the gas-pressure-medium apparatus. A new generation of solid-medium piston-cylinder ("Griggs-type") apparatus is here described. Able to perform high-pressure deformation experiments up to 5 GPa and designed to adapt an internal load cell, such a new apparatus offers the potential to establish a technological basis for high-pressure rheology. This paper provides video-based detailed documentation of the procedure (using the "conventional" solid-salt assembly) to perform high-pressure, high-temperature experiments with the newly designed Griggs-type apparatus. A representative result of a Carrara marble sample deformed at 700 °C, 1.5 GPa and 10-5 s-1 with the new press is also given. The related stress-time curve illustrates all steps of a Griggs-type experiment, from increasing pressure and temperature to sample quenching when deformation is stopped. Together with future developments, the critical steps and limitations of the Griggs apparatus are then discussed.

High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus.

In order to address geological processes at great depths, rock deformation should ideally be tested at high pressure (> 0.5 GPa) and high temperature (> 300 °C). However, because of the low stress resolution of current solid-pressure-medium apparatuses, high-resolution measurements are today restricted to low-pressure deformation experiments in the gas-pressure-medium apparatus. A new generation of solid-medium piston-cylinder ("Griggs-type") apparatus is here described. Able to perform high-pressure deformation experiments up to 5 GPa and designed to adapt an internal load cell, such a new apparatus offers the potential to establish a technological basis for high-pressure rheology. This paper provides video-based detailed documentation of the procedure (using the "conventional" solid-salt assembly) to perform high-pressure, high-temperature experiments with the newly designed Griggs-type apparatus. A representative result of a Carrara marble sample deformed at 700 °C, 1.5 GPa and 10-5 s-1 with the new press is also given. The related stress-time curve illustrates all steps of a Griggs-type experiment, from increasing pressure and temperature to sample quenching when deformation is stopped. Together with future developments, the critical steps and limitations of the Griggs apparatus are then discussed.

Quantitative analysis of vortex added-mass and impulse generation during vortex ring formation based on elliptic Lagrangian coherent structures

In many propulsive systems operating with the generation of large-scale vortices, the enhanced performance is achieved and closely related with the effects of vortex added-mass. However, quantitatively analysing vortex added-mass is difficult, particularly when the vortex is significantly deforming, because identifying a physical vortex boundary is difficult. Recently, a physical vortex boundary is defined by the elliptic Lagrangian coherent structures (LCSs), which are sought as closed stationary curves of the averaged Lagrangian strain. In this study, a canonical vortex-ring flow is investigated to analyze the evolution of vortex added-mass by examining the evolution of elliptic LCSs. A vortex ring is produced experimentally by employing a piston-cylinder apparatus, and the time-dependent flow fields are recorded by particle image velocimetry technique. Elliptic LCSs are computed with high-precision algorithms. Compared with the streamline pattern and ridges of the finite-time Lyapunov exponent, elliptic LCSs can more precisely and quantitatively determine a vortex boundary that acts as a material surface in fluids. In terms of elliptic LCSs, vortex added-mass coefficient is computed and demonstrates a decreasing tendency from approximately 1.3–0.88 during vortex ring formation. Correspondingly, the overpressure contribution to the vortex impulse exhibits the same decreasing tendency with the vortex added-mass coefficient, because the production of overpressure is largely owing to the effects of vortex added-mass. Actually, elliptic LCSs have provided us a powerful tool to determine the vortex added-mass coefficient. In addition, a potential implication of these results is that elliptic LCSs can be used to estimate instantaneous force based on vortex momentum and vortex added-mass.

Intracrystalline “geothermometry” assessed on clino and orthopyroxene bearing synthetic rocks

Recent discussion on the application of intracrystalline “geothermometers” based on the Fe–Mg order-disorder reaction in pyroxene in natural rocks, indicates that the available calibration equations for clino and orthopyroxenes (cpx and opx), which express the equilibrium intracrystalline Fe–Mg distribution coefficient kD(Fe–Mg) as a function of temperature, require independent validation.In this paper, we tested the available experimental calibrations for clino and orthopyroxenes by determining the site occupancies of these minerals in synthetic samples grown from a hydrous nepheline basanite in a piston-cylinder apparatus at 1050 °C at 2.0 GPa to 1170 °C at 3.0 GPa, and quenched very rapidly by shutting off the power. The site occupancies were determined by single crystal X-ray diffraction (SC-XRD) and used to calculate the closure temperature, TC, of cation ordering using available calibrations of kD(Fe–Mg) vs. T. The calculated TC values of both clino and orthopyroxenes were found to be close to the temperatures at which they were quenched, in line with expected kinetic behavior, when calibrations for cpx (Murri et al., 2016) and opx (Stimpfl et al., 2005) based on SC-XRD structure refinements were used. In particular, the smallest discrepancy between calculated and actual temperature is of the order of a few degrees (12 °C for cpx and 4 °C for opx), and the largest is of the order of tens of degrees (22 °C for cpx and 55 °C for opx). On the other hand, much lower TCs were obtained when calibrations based on Mössbauer determination of site occupancies were used.These results confirm that the two methods (i.e. SC-XRD and Mössbauer) give inherently different site occupancy data and that the same methodology should thus be used for both calibration and natural samples in the determination of cooling rate of host rocks.

Experimental investigation of the reaction between corundum xenocrysts and alkaline basaltic host magma: Constraints on magma residence times of basalt-hosted sapphires

Megacrystic sapphires (Fe-Ti-rich corundum) of up to 5 cm in size are well known from alkaline mafic rocks from intra-continental rift-related magmatic fields. There is no doubt that these sapphires represent xenocrysts that were trapped from their original lithology by ascending basaltic magmas carrying them to the Earth's surface. Most studies about basalt-hosted sapphires address the question about the origin of the sapphires, but there is hardly any information available about the time the sapphires resided inside the carrier melt. Sapphires are in reaction relationship with basalt and produce spinel coronas at the sapphire-basalt interface, spatially separating the mutually incompatible phases from one another. Assuming isothermal and isobaric conditions of spinel rim formation, the rim-thickness should be a function of the reaction time with the basaltic melt. In this paper, we report time-series experiments aimed at investigating the kinetics of spinel rim formation due to igneous corrosion of corundum. Therefore, we reacted corundum fragments with alkaline basalt powder at 1250 °C and 1GPa, using a Piston Cylinder Apparatus. The width of the spinel rim was used to estimate a residence time. Extrapolating the experimentally derived reaction rates to the thickness of natural spinel rims as described from the Siebengebirge Volcanic Field, Germany, and from Changle, China, we estimated residence times in the order of a few weeks to months.

First measurements of OH-C exchange and temperature-dependent partitioning of OH and halogens in the system apatite–silicate melt

We present the first integrated study of carbonate, hydroxyl, fluoride, and chloride ion partitioning in the apatite-melt system. We determined volatile partitioning behavior between apatite and silicate melt for both haplobasaltic andesite and trachyte bulk compositions at 0.5–1 GPa and 1250°C using the piston-cylinder apparatus. All volatile species were analyzed directly in both apatite and glass using secondary ion mass spectrometry (SIMS) and electron probe microanalysis. Distribution coefficients for OH-halogen exchange are similar to those from previous studies, and together with literature data, reveal a significant log-linear relationship with temperature, while the effects of pressure and melt composition are minimal. Meanwhile, halogen-free experiments generate very high C contents (up to 5000 ppm) in apatite. Stoichiometry calculations and infrared spectra indicate that this C is mainly incorporated onto the channel volatile site together with hydroxyl. In halogen-bearing experiments, apatite crystals contain significantly lower C (≤500 ppm), which may be partly incorporated onto the phosphate site while the channel volatile site is filled by OH+F+Cl+C. Our experiments give the first constraints on H2O-CO2 exchange between apatite and silicate melt, with a KD of 0.355 ± 0.05 for the trachyte and 0.629 ± 0.08 for the haplobasaltic andesite. The new constraints on the temperature-dependence of partitioning will enable quantitative modeling of apatite-volatile exchange in igneous systems, while this new partitioning data and method for direct, in situ analysis of C in apatite mark a significant advance that will permit future studies of magmatic C and other volatiles. This has a broad range of potential applications including magmatic differentiation, fractionation, and degassing; quantification of volatile budgets in extraterrestrial and deep earth environments; and mineralization processes.

Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure

We employed ab initio evolutionary algorithm USPEX to speed up the discovery of a novel oxynitride in the binary system of GaN-TiO2 using high-pressure synthesis. A 1:2 mixture of GaN and nanocrystalline TiO2 (anatase) was reacted under 1 GPa of pressure and at 1200 °C in a piston cylinder apparatus to produce a mixture of TiO2 (rutile) and an unknown phase. From the initial analysis of high resolution neutron and X-ray diffraction data, it is isomorphic with monoclinic V2GaO5 with a unit cell composition of Ga10Ti8O28N2 with the following parameters: monoclinic, space group C2/m, a = 17.823(1) A, b = 2.9970(1) A, c = 9.4205(5) A, β = 98.446(3)°; Volume = 497.74(3) A3. Further, a joint rietveld refinement revealed two distinct regimes—A Ti-rich block and a Ga-rich block. The Ti-rich block consists of four edge-shared octahedra and contains a site which is about 60% occupied by N; this site is bonded to four Ti. The remainder of the block consists of edge linked Ti-octahedral chains linked to the TiN/TiO fragments at octahedral corners partially occupied by nitrogen. The Ga-block contains two symmetry independent octahedral sites, occupied mostly by Ga, and a pure Ga-centered tetrahedral site bonded mostly to oxygen.

On the formation modes in vortex interaction for multiple co-axial co-rotating vortex rings

Interaction among multiple vortices is of particular importance to biological locomotion. It plays an essential role in the force and energy capture. This study examines the motion and dynamics of multiple co-axial co-rotating vortex rings. The vortex rings, which have the same formation time, are successively generated in a piston-cylinder apparatus by accurately controlling the interval time. The flow fields are visualized by the finite-time Lyapunov exponent and then repelling Lagrangian coherent structures (r-LCSs) are determined. Two types of vortex interactions (“strong” and “weak”) are defined by investigating the r-LCSs: a strong interaction is indicated by connected r-LCSs showing a channel for fluid transport (termed as a “flux window”); a weak interaction is indicated by disconnected r-LCSs between the vortex rings. For strong interaction, leapfrogging and merger of vortex rings can happen in the later stage of the evolution process; however, the rings are separated for weak interaction. Two distinct formation modes, the formation enhancement mode (FEM) and formation restraint mode (FRM), refer to the effect of one or multiple vortex ring(s) on the initial circulation of the subsequently formed vortex ring. In the FEM, the circulation of a vortex ring is larger than that of an isolated (without interaction) vortex ring. On the other hand, the situation is opposite in the FRM. A dimensionless number reflecting the interaction mechanism, “structure stretching number” S*, is proposed, which evaluates the induced effect of the wake vortices on the formation of a vortex ring. A limiting S* (SL*=(2±0.4)×10−4) is the bifurcation point of the two formation modes. The augmentation of circulation reaches up to 10% for the FEM when S*<SL*, while in the FRM (S*>SL*), the circulation decreases for at most 20%. The newly defined formation modes and number could shed light on the understanding of the dynamics of multiple vortex ring flows.

Synthesis of monticellite\u2013forsterite and merwinite\u2013forsterite symplectites in the CaO\u2013MgO\u2013SiO2 model system: influence of temperature and water content on microstructure evolution

Homogeneous single crystals of synthetic monticellite with the composition {text{Ca}}_{0.88}{text{Mg}}_{1.12}{text{SiO}}_4 (Mtc I) were annealed in a piston-cylinder apparatus at temperatures between 1000 and 1200,^{circ }hbox {C}, pressures of 1.0–1.4 GPa, for run durations from 10 min to 24 h and applying bulk water contents ranging from 0.0 to 0.5 wt% of the total charge. At these conditions, Mtc I breaks down to a fine-grained, symplectic intergrowth. Thereby, two types of symplectites are produced: a first symplectite type (Sy I) is represented by an aggregate of rod-shaped forsterite immersed in a matrix of monticellite with end-member composition (Mtc II), and a second symplectite type (Sy II) takes the form of a lamellar merwinite–forsterite intergrowth. Both symplectites may form simultaneously, where the formation of Sy I is favoured by the presence of water. Sy I is metastable with respect to Sy II and is successively replaced by the latter. For both symplectite types, the characteristic spacing of the symplectite phases is independent of run duration and is only weeakly influenced by the water content, but it is strongly temperature dependent. It varies from about 400 nm at 1000,^{circ }hbox {C} to 1200 nm at 1100,^{circ }hbox {C} in Sy I, and from 300 nm at 1000,^{circ }hbox {C} to 700 nm at 1200,^{circ }hbox {C} in Sy II. A thermodynamic analysis reveals that the temperature dependence of the characteristic spacing of the symplectite phases is due to a relatively high activation energy for chemical segregation by diffusion within the reaction front as compared to the activation energy for interface reactions at the reaction front. The temperature dependence of the characteristic lamellar spacing and the temperature-time dependence of overall reaction progress have potential for applications in geo-thermometry and geo-speedometry.

Zircon/fluid trace element partition coefficients measured by recrystallization of Mud Tank zircon at 1.5 GPa and 800–1000 °C

Hydrothermal zircon grains have trace element characteristics such as low Th/U, high U, and high rare earth element (REE) concentrations that distinguish them from magmatic, metamorphic, and altered zircon grains, but it is unclear whether these characteristics result from distinctive fluid compositions or zircon/fluid fractionation effects. New experiments aimed at measuring zircon/fluid trace element partition coefficients Dz/f involved recrystallizing natural Mud Tank zircon with low trace element concentrations in the presence of H2O, 1 m NaOH, or 1 m HCl doped with ∼1000 ppm of rare earth elements (REE), Y, U and Th and ∼500 ppm of Li, B, P, Nb, Ba, Hf, and Ta. Experiments were run for 168 h at 1.5 GPa, 800–1000 °C, and fO2 = NNO in a piston cylinder apparatus using the double capsule method. LA-ICP-MS analysis shows that run product zircon crystals have much higher trace element concentrations than in Mud Tank zircon starting material. Dz/f values were estimated from run product zircon analyses and bulk composition using mass balance.Most elements behave incompatibly, with median Dz/f being highest for Hf = 8 and lowest for B = 0.02. Addition of NaOH or HCl had little influence on Dz/f values. Dz/f for LREE are anomalously high, likely due to contamination of run product zircon with quenched solutes enriched in incompatible elements, so DLREE were estimated using lattice strain theory. Brice curves for +3 ions yield zircon/fluid DLu/DLa of ∼800–5000. A Brice curve fit to +4 ions yielded DCe4+ values. Estimated concentrations of Ce3+ and Ce4+ show that the average Ce4+/Ce3+ in zircon of 27 is much higher than in fluid of 0.02. Th and U show little fractionation, with median DTh/DU = 0.7, indicating that the low Th/U in natural hydrothermal zircon is inherited from the fluid. Natural fluid compositions estimated from measured Dz/f and published compositions of hydrothermal zircon grains from aplite and eclogite reflect the mineralogy of the host rock, e.g., fluid in equilibrium with eclogite garnet is depleted in heavy REE relative to middle REE, and has low Th/U.

Experimental determination of magnesia and silica solubilities in graphite-saturated and redox-buffered high-pressure COH fluids in equilibrium with forsterite + enstatite and magnesite + enstatite

We experimentally investigated the dissolution of forsterite, enstatite and magnesite in graphite-saturated COH fluids, synthesized using a rocking piston cylinder apparatus at pressures from 1.0 to 2.1 GPa and temperatures from 700 to 1200 °C. Synthetic forsterite, enstatite, and nearly pure natural magnesite were used as starting materials. Redox conditions were buffered by Ni–NiO–H2O (ΔFMQ = − 0.21 to − 1.01), employing a double-capsule setting. Fluids, binary H2O–CO2 mixtures at the P, T, and fO2 conditions investigated, were generated from graphite, oxalic acid anhydrous (H2C2O4) and water. Their dissolved solute loads were analyzed through an improved version of the cryogenic technique, which takes into account the complexities associated with the presence of CO2-bearing fluids. The experimental data show that forsterite + enstatite solubility in H2O–CO2 fluids is higher compared to pure water, both in terms of dissolved silica (mSiO2 = 1.24 mol/kgH2O versus mSiO2 = 0.22 mol/kgH2O at P = 1 GPa, T = 800 °C) and magnesia (mMgO = 1.08 mol/kgH2O versus mMgO = 0.28 mol/kgH2O) probably due to the formation of organic C–Mg–Si complexes. Our experimental results show that at low temperature conditions, a graphite-saturated H2O–CO2 fluid interacting with a simplified model mantle composition, characterized by low MgO/SiO2 ratios, would lead to the formation of significant amounts of enstatite if solute concentrations are equal, while at higher temperatures these fluid, characterized by MgO/SiO2 ratios comparable with that of olivine, would be less effective in metasomatizing the surrounding rocks. However, the molality of COH fluids increases with pressure and temperature, and quintuplicates with respect to the carbon-free aqueous fluids. Therefore, the amount of fluid required to metasomatize the mantle decreases in the presence of carbon at high P–T conditions. COH fluids are thus effective carriers of C, Mg and Si in the mantle wedge up to the shallowest level of the upper mantle.

The isotope mass effect on chlorine diffusion in dacite melt, with implications for fractionation during bubble growth

Previous experimental studies have revealed that the difference in diffusivity of two isotopes can be significant in some media and can lead to an observable fractionation effect in silicate melts based on isotope mass. Here, we report the first characterization of the difference in diffusivities of stable isotopes of Cl (35Cl and 37Cl). Using a piston–cylinder apparatus, we generated quenched melts of dacitic composition enriched in Cl; from these we fabricated diffusion couples in which Cl atoms were induced to diffuse in a chemical gradient at 1200 to 1350 °C and 1 GPa. We analyzed the run products by secondary ion mass spectrometry (SIMS) for their isotopic compositions along the diffusion profiles, and we report a diffusivity ratio for 37Cl/35Cl of 0.995±0.001 (β=0.09±0.02). No significant effect of temperature on the diffusivity ratio was discernable over the 150 °C range covered by our experiments. The observed 0.5% difference in diffusivity of the two isotopes could affect our interpretation of isotopic measurements of Cl isotopes in bubble-bearing or degassed magmas, because bubble growth is regulated in part by the diffusive supply of volatiles to the bubble from the surrounding melt. Through numerical simulations, we constrain the extent of Cl isotopic fractionation between bubble and host melt during this process. Bubble growth rates vary widely in nature—which implies a substantial range in the expected magnitude of isotopic fractionation—but plausible growth scenarios lead to Cl isotopic fractionations up to about 5‰ enrichment of 35Cl relative to 37Cl in the bubble. This effect should be considered when interpreting Cl isotopic measurements of systems that have experienced vapor exsolution.