Fluid Melt Research Articles

The application of thermodynamic perturbation theory to the calculation of excess free energy of small systems: 1. The study of the dimensional dependence of specific free energy of small droplets

Fundamentals of the application of the method of thermodynamic perturbation theory to finding the excess free energy of small objects were analyzed. The size dependence of the specific surface free energy of small droplets of a simple Lennard-Jones fluid, water, and metal melts was studied in the first and second approximations of the perturbation theory. It was established that, for all studied systems, the size dependence of the surface tension was satisfactorily described by Tolman’s formula. At small particle radii, Rusanov’s formula was well fulfilled.

Partitioning of boron among melt, brine and vapor in the system haplogranite–H 2O–NaCl at 800 °C and 100 MPa

Fluid-saturated experiments were conducted to investigate the partitioning of boron among haplogranitic melt, aqueous vapor and brine at 800 °C and 100 MPa. Experiments were carried out in cold-seal pressure vessels for 1 to 21 days, and utilized powdered synthetic subaluminous haplogranite glass doped with 1000 ppm B (crystalline H 3BO 3) and variable amounts of NaCl and H 2O at a fluid/haplogranite mass ratio=1:1. Run-product glasses were analyzed for boron concentration by secondary ion mass spectrometry (SIMS) and for major elements and chlorine by electron microprobe. The composition of the coexisting fluid was calculated by mass balance. Boron partition coefficients between aqueous vapor and hydrous granitic melt range from 3.1 to 6.3, and demonstrate a clear preference of boron for the vapor over the hydrous melt. Partition coefficients between brine and hydrous granitic melt vary from 0.45 to 1.1, suggesting that boron has no preference for the brine or the melt. The bulk fluid–melt partition coefficients for low-salinity and high-salinity experiments are D B (vapor/melt)=4.6±1.3 and D B (brine/melt)=0.91±0.49, respectively. The corresponding vapor–brine partition coefficient is 5.0±3.1, demonstrating that boron partitions preferentially into the vapor over the brine at the conditions of this study. The preferential incorporation of boron in the aqueous vapor is controlled by borate speciation and solution mechanism. The dominant borate species in aqueous fluids, H 3BO 3 o, is highly soluble in aqueous vapor ( X B 2O 3 =0.187); however, B 2O 3 is immiscible in NaCl liquid. Consequently, concentrations of boron in aqueous vapor are significantly higher than in the coexisting brine. Furthermore, Na–B complexing in the melt at high chlorine fluid contents stabilizes boron in the melt thereby contributing to the non-preferential partitioning of boron between brine and melt. The commonly observed association of tourmalinization (boron metasomatism), brecciation and ore deposition in nature is consistent with the preferential partitioning of boron into aqueous vapor of magmatic-hydrothermal systems predicted by this study.

Mechanisms and rates of quartz dissolution in melts in the CMAS (CaO?MgO?Al2O3?SiO2) system

The dissolution rate of minerals in silicate melts is generally assumed to be a function of the rate of mass transport of the released cations in the solvent. While this appears to be the case in moderately to highly viscous solvents, there is some evidence that the rate-controlling step may be different in very fluid, highly silica undersaturated melts such as basanites. In this study, convection-free experiments using solvent melts with silica activity from 0.185–0.56 and viscosity from 0.03–4.6 Pa s show that the dissolution rate is strongly dependent on the degree of superheating, silica activity and the viscosity of the solvent. Dissolution rates increase with increasing melt temperature and decreasing silica activity and viscosity. Quartz dissolution in melts with viscosity <0.59–1.9 Pa s and silica activity <0.47 is controlled by the rate of interface reaction as shown by the absence of steady state composition and silica saturation in the interface melts. Only in the most viscous melt with the highest silica activity is quartz dissolution controlled by the rate of diffusion in the melt and only after a long initiation time. The results of this study indicate that although a diffusion-based model may be applicable to dissolution in viscous magmas, a different approach that combines the interplay between the degree of undersaturation of the melt and its viscosity is required in very fluid melts.

Simple method for theoretical estimation of viscosity of oxide melts using optical basicity

Numerous models have been reported in the literature for theoretical estimation of the viscosity of molten slags and glasses. These models, however, generally employ various empirical constants, often a large number, derived from actual experimental data. The model popularised by Urbain employs two interrelated constants to express the variation of viscosity with temperature. One constant is estimated on the basis of melt composition, employing again several empirical constants. The present communication reveals a novel and elegant method which allows theoretical estimation using Urbain's equation that employs two interrelated constants. However, it is shown that these constants are empirically related to optical basicity. Thus, a new method of estimation of viscosity is proposed, which makes it possible to calculate viscosity based on only optical basicity of the melt calculated from the melt composition. The model proposed is applicable to homogeneous fluid melts.

Freezing/melting behaviour within carbon nanotubes

We report a study of the freezing and melting of fluids confined within multi-walled carbon nanotubes with an internal diameter of 5 nm, using experimental measurements and molecular simulations. Dielectric relaxation spectroscopy was used to determine the experimental melting points and relaxation times of nitrobenzene and carbon tetrachloride within carbon nanotubes, and parallel tempering Monte Carlo simulations in the grand canonical ensemble were performed for confined carbon tetrachloride. The simulations show that the adsorbate forms concentric layers that solidify into quasi-two-dimensional hexagonal crystals with defects; highly defective microcrystalline regions are formed in the inner layers, owing to the strong geometrical constraints. Our simulations show no formation of common three-dimensional crystalline structures (fcc, hcp, bcc, sc or icosahedral) in confinement. The results suggest the presence of inhomogeneous phases (i.e., combinations of crystalline and liquid regions) within the pore over extended temperature ranges. Our results indicate that the outer layers of adsorbate solidify at temperatures slightly higher than the bulk freezing point, whereas the inner layers freeze at lower temperatures. The simulation results are in good agreement with the experimental measurements.

Freeze or dehydrate: only two options for the survival of subzero temperatures in the arctic enchytraeid Fridericia ratzeli.

Hygrophilic soil animals, like enchytraeids, overwintering in frozen soil are unlikely to base their cold tolerance on supercooling of body fluids. It seems more likely that they will either freeze due to inoculative freezing, or dehydrate and adjust their body fluid melting point to ambient temperature as has been shown for earthworm cocoons and Collembola. In the present study we tested this hypothesis by exposing field-collected adult Fridericia ratzeli from Disko, West Greenland, to freezing temperatures under various moisture regimes. When cooled at -1 degrees C min(-1) under dry conditions F. ratzeli had a mean temperature of crystallisation ( T(c)) of -5.8 degrees C. However, when exposed to temperatures above standard T(c) for 22 h, at -4 degrees C, most individuals (90%, n= 30) remained unfrozen. Slow cooling from -1 degrees C to -6 degrees C in vials where the air was in equilibrium with the vapour pressure of ice resulted in freezing in about 65% of the individuals. These individuals maintained a normal body water content of 2.7-3.0 mg mg(-1) dry weight and had body fluid melting points of about -0.5 degrees C with little or no change due to freezing. About 35% of the individuals dehydrated drastically to below 1.1 mg mg(-1) dry weight at -6 degrees C, and consequently had lowered their body fluid melting point to ca. -6 degrees C at this time. Survival was high in both frozen and dehydrated animals at -6 degrees C, about 60%. Approximately 25% of the animals (both frozen and dehydrated individuals) had elevated glucose concentrations, but the mean glucose concentration was not increased to any great extent in any group due to cold exposure. The desiccating potential of ice was simulated using aqueous NaCl solutions at 0 degrees C. Water loss and survival in this experiment were in good agreement with results from freezing experiments. The influence of soil moisture on survival and tendency to dehydrate was also evaluated. However, soil moisture ranging between 0.74 g g(-1) and 1.15 g g(-1) dry soil did not result in any significant differences in survival or frequency of dehydrated animals even though the apparent wetness and structure of the soil was clearly different in these moisture contents.

Characteristics of melt inclusions in skarn minerals from Fe, Cu(Au) and Au(Cu) ore deposits in the region from Daye to Jiujiang

A vast amount of the melt inclusions and fluid-melt inclusions have been found in skarn minerals from Fe, Cu(Au) and Au(Cu) ore deposits distributed from Daye to Jiujiang along the Yangtze River besides vapor-liquid inclusions. The melt inclusions are many and varied in shape. They mainly consist of crystallized silicate phases (Csi), iron phases (Fe), amorphous silicate phases (Asi) and vapor (V) with different volume percentages, and some of them contain several crystallized silicate phases. These melt inclusion sizes are commonly (10—46) × (6—15) μm2. A difference between the fluid-melt inclusions and melt inclusions is that the liquid phase appears in the former and their homogenization temperatures are lower than the latter. We measured the homogenization temperatures of the melt inclusions, fluid-melt inclusions and fluid inclusions in ten thin sections from eight ore deposits on Leitz microscope heating stage 1350 which was made in Germany. Forty-eight homogenization temperature values have been obtained. Among them, thirty-nine values are homogenization temperatures of the melt inclusions in garnet and pyroxene from skarns, two values are homogenization temperatures of fluid-melt inclusions, others belong to the fluid inclusions. Melt inclusions in garnet and pyroxene have homogenization temperatures of 890—1115°C. Fluid-melt inclusions have homogenization temperatures of 745—750°C. Homogenization temperatures of fluid inclusions are between 580°C and 675°C. The average of thirtynine homogenization temperatures for the melt inclusions is 1029.9°C. We think studied skarns to be magmatic genesis on the basis of available data relative to the characteristic features of phase states within the melt inclusions and the fluid melt inclusions and their homogenization temperatures.

Process Intensification in Particle Technology: Intensive Granulation of Powders by Thermomechanically Induced Melt Fracture

Process intensification in particle technology is illustrated by a novel continuous agglomeration and microencapsulation (granulation) technique based on the thermomechanically induced melt fracture. This intensive structuring method is based on the nonisothermal flow-induced phase inversion phenomenon in which the continuous phase of the fluid (poly(ethylene glycol) melt) undergoes fractional solidification, thus essentially increasing the volume fraction of the solid phase during passage between two disks. The polymer melt containing the filler particles (calcium carbonate) is fed centrally (using an extruder) into the gap between two disks, one of which is stationary (stator) while the other rotates (rotor) at a constant angular velocity. These disks have several sets of cavities formed in such a way that the upper and lower cavities never match during rotation and that they can achieve mixing as well as pumping. The rotor and stator are kept at different temperatures so as to allow the cooling of the ...

Genesis of primitive, arc-type basalt: Constraints from Re, Os, and Cl on the depth of melting and role of fluids

Research Article| July 01, 2002 Genesis of primitive, arc-type basalt: Constraints from Re, Os, and Cl on the depth of melting and role of fluids Kevin Righter; Kevin Righter 1Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar John T. Chesley; John T. Chesley 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Joaquin Ruiz Joaquin Ruiz 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Kevin Righter 1Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA John T. Chesley 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Joaquin Ruiz 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Publisher: Geological Society of America Received: 26 Feb 2002 Revision Received: 23 Mar 2002 Accepted: 28 Mar 2002 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2002) 30 (7): 619–622. https://doi.org/10.1130/0091-7613(2002)030<0619:GOPATB>2.0.CO;2 Article history Received: 26 Feb 2002 Revision Received: 23 Mar 2002 Accepted: 28 Mar 2002 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kevin Righter, John T. Chesley, Joaquin Ruiz; Genesis of primitive, arc-type basalt: Constraints from Re, Os, and Cl on the depth of melting and role of fluids. Geology 2002;; 30 (7): 619–622. doi: https://doi.org/10.1130/0091-7613(2002)030<0619:GOPATB>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The general model for arc-type basalt genesis is that subducted plates reach a certain depth and release their fluids in a series of dehydration reactions. The fluid migrates into the overlying mantle wedge and initiates melting. High 187Os/188Os ratios in some arc magmas have been attributed to this fluid. Although this interpretation follows logically from the general model for arc-type basalt genesis, it is not supported by experimental data or by Re, Os, or Cl data for arc-type basalt, eclogites, and peridotites. Our new data for basaltic rocks from the Mexican volcanic belt together with data from several other arcs lead us to propose that subduction fluids contain only minimal Re, Os, and Cl, and therefore that 187Os/188Os is not increased significantly in the melts above 0.145. The observed low Re concentrations are best explained by initiation of arc-basalt melting in the garnet stability field. Retention of Re by garnet in the source will deplete arc-type basalts in Re relative to oceanic-island basalt and mid-ocean-ridge basalt. Radiogenic Os measured in many arc-type basalts is most likely due to crustal interaction rather than a subduction fluid with high and radiogenic Os concentrations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Thermotropic liquid crystalline copolyesters with non-coplanar biphenylene units tailored for blend fiber processing with PET

Via melt polycondensation two series of liquid crystalline thermotropic polyesters were synthesized for in situ reinforcement components in PET blend fibers. The copolymerization of a monomer bearing a bulky side group (tert-butyl hydrochinone) or a crankshaft monomer (6-acetoxy-2-naphthoic acid) with the non-coplanar 2,2′-dimethyl biphenol and terephthalic acid yielded two fully aromatic thermotropic polyesters. By varying and adjusting the individual monomer compositions, the melting behavior can be tailored to match the PET processing window. Solution viscosities up to ηinh=6.57dl/g were achieved. By thermal characterization with DSC in combination with polarization microscopy up to 310°C neither a crystal melting point nor an isotropic transition was detected. Hence, the nematic polyesters solidify below the glass transition temperature into a glassy solid without crystallization. The polyesters are thermally stable above 400°C and form fluid melts. Fibers were spun from both series. Optimal processing was encountered at polyesters containing 60mol% HNA, which could be spun continuously into high quality fibers. The fibers were characterized by tensile test, WAXS, and SEM. Fiber orientation was improved at a higher draw-down ratio and the Young's modulus was determined to 49GPa at a tenacity of 550MPa.

Fluid inclusions in mantle xenoliths

Fluid inclusions in olivine and pyroxene in mantle-derived ultramafic xenoliths in volcanic rocks contain abundant CO 2-rich fluid inclusions, as well as inclusions of silicate glass, solidified metal sulphide melt and carbonates. Such inclusions represent accidentally trapped samples of fluid- and melt phases present in the upper mantle, and are as such of unique importance for the understanding of mineral–fluid–melt interaction processes in the mantle. Minor volatile species in CO 2-rich fluid inclusions include N 2, CO, SO 2, H 2O and noble gases. In some xenoliths sampled from hydrated mantle-wedges above active subduction zones, water may actually be a dominant fluid species. The distribution of minor volatile species in inclusion fluids can provide information on the oxidation state of the upper mantle, on mantle degassing processes and on recycling of subducted material to the mantle. Melt inclusions in ultramafic xenoliths give information on silicate–sulphide–carbonatite immiscibility relationships within the upper mantle. Recent melt-inclusion studies have indicated that highly silicic melts can coexist with mantle peridotite mineral assemblages. Although trapping-pressures up to 1.4 GPa can be derived from fluid inclusion data, few CO 2-rich fluid inclusions preserve a density representing their initial trapping in the upper mantle, because of leakage or stretching during transport to the surface. However, the distribution of fluid density in populations of modified inclusions may preserve information on volcanic plumbing systems not easily available from their host minerals. As fluid and melt inclusions are integral parts of the phase assemblages of their host xenoliths, and thus of the upper mantle itself, the authors of this review strongly recommend that their study is included in any research project relating to mantle xenoliths.

Deep fluids in subduction zones

The fluid inclusions preserved in high and ultrahigh pressure rocks provide direct information on the compositions of fluid phases evolved during subduction zone metamorphism, and on fluid–rock interactions occurring in such deep environments. Recent experiments and petrologic studies of eclogite–facies rocks demonstrate that stability of a number of hydrous phases in all rock systems allows fluid transport into the mantle sources of arc magmas, as well as into much deeper levels of the Earth's mantle. In eclogite–facies rocks, the presence of large ion lithophile elements (LILE) and light rare earths (LREE)-bearing hydrous phases such as epidote and lawsonite, together with HFSE repositories as rutile and other Ti-rich minerals, controls the trace element budget of evolved fluids and fluid-mediated cycling of slab components into the overlying mantle. Studies of fluid inclusions in eclogite–facies terrains suggest that subduction mainly evolves aqueous solutions, melts being produced only locally. Eclogite-facies rocks diffusely record processes of fluid–melt–rock interactions that exerted considerable control on the element and volatile budget of subduction fluids. Trace element fractionation during such interactions needs to be tested and quantified in more detail to achieve the ultimate compositions actually attained by fluids leaving off the slab. Variably saline inclusions with minor CO 2 and N 2 are trapped in rock-forming high pressure minerals; brines with up to 50% by weight dissolved solute are diffusely found in veins. The latter inclusions are residues after fluid–rock interactions and deposition of complex vein mineralogies: this evidence suggests increased mineral solubility into the fluid and formation, at a certain stage, of silicate-rich aqueous solutions whose geochemical behaviour and transport capacity can approach that of a melt phase. This is supported by experimental work showing high solubility of silicate components in fluids at high pressures. However, natural examples of inclusions trapping such a fluid and quantitative analyses of its major and trace element composition are not yet available. Fluids in high and very high pressure rocks do not move over large scales and the channelways of fluid escape from the slab are not yet identified. This suggests that only part of the slab fluid is lost and returned to the surface via magmatism; the remaining trapped fraction being subducted into deeper levels of the upper mantle, to renew its budget of substances initially stored in the exosphere.

Melt inclusions in pegmatite quartz: complete miscibility between silicate melts and hydrous fluids at low pressure

Fluorine-, boron- and phosphorus-rich pegmatites of the Variscan Ehrenfriedersdorf complex crystallized over a temperature range from about 700 to 500 °C at a pressure of about 1 kbar. Pegmatite quartz crystals continuously trapped two different types of melt inclusions during cooling and growth: a silicate-rich H2O-poor melt and a silicate-poor H2O-rich melt. Both melts were simultaneously trapped on the solvus boundaries of the silicate (+ fluorine + boron + phosphorus) − water system. The partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 °C in steps of 50 °C by conventional rapid-quench hydrothermal experiments. Glasses of completely rehomogenized inclusions were analyzed for H2O by Raman spectroscopy, and for major and some trace elements by EMP (electron microprobe). Both types of melt inclusions define a solvus boundary in an XH2O–T pseudobinary system. At 500 °C, the silicate-rich melt contains about 2.5 wt% H2O, and the conjugate water-rich melt about 47 wt% H2O. The solvus closes rapidly with increasing temperature. At 650 °C, the water contents are about 10 and 32 wt%, respectively. Complete miscibility is attained at the critical point: 712 °C and 21.5 wt% H2O. Many pegmatites show high concentrations of F, B, and P, this is particularly true for those pegmatites associated with highly evolved peraluminous granites. The presence of these elements dramatically reduces the critical pressure for fluid–melt systems. At shallow intrusion levels, at T ≥ 720 °C, water is infinitely soluble in a F-, B-, and P-rich melt. Simple cooling induces a separation into two coexisting melts, accompanied with strong element fractionation. On the water-rich side of the solvus, very volatile-rich melts are produced that have vastly different physical properties as compared to “normal” silicate melts. The density, viscosity, diffusivity, and mobility of such hyper-aqueous melts under these conditions are more comparable to an aqueous fluid.

Immobilization of CsCl and SrF 2 in iron phosphate glass

A large part of the radioactive 137Cs and 90Sr stored at the Hanford site is present as CsCl and SrF 2. Attempts to incorporate halides in borosilicate glass often produces immiscibility which is undesirable for immobilizing nuclear materials. Conversely, iron phosphate glasses have been made with up to 26 and 31 mol% CsCl and SrF 2, respectively, and up to 34 mol% CsCl and SrF 2 combined. These compositions are melted at temperatures as low as 950°C for 2 h and form fluid melts. The low melting temperature of the iron phosphate wasteforms reduces the probability that radioactive 137Cs will vaporize from the melt, which becomes increasingly likely at the higher temperature (⩾1150° C) used to melt borosilicate glasses. Analysis of the glasses produced in this study show that very little, if any, Cs and Sr was volatilized from the batches, although the majority of the halide is released during melting. All of the iron phosphate glassy wasteforms in the current study had a total ion release in distilled water of approximately 10 mg/l which is about one tenth that measured for the approved reference material (ARM-1), a reference borosilicate glass. The dissolution rate of the iron phosphate wasteforms in distilled water decreased with increasing iron content.

Fluorite [formula omitted] and REE constraints on fluid–melt relations, crystallization time span and bulk DSr of evolved high-silica granites. Tabuleiro granites, Santa Catarina, Brazil

The evolved high-silica Tabuleiro granites within the Early Paleozoic Santa Catarina Composite Massif, Pelotas Batholith, southern Brazil are characterized by the presence of euhedral to subeuhedral accessory fluorite and geochemical features typical of topaz–rhyolites and related A-type granites. Sr isotopes and REE data of the Tabuleiro granites and their accessory fluorite are used to constrain fluid–melt relations, crystallization time span and bulk crystal–melt Sr partition coefficient D Sr.Correlations involving REE, Eu/Eu*, Rb/Sr, Sr and 87 Sr/ 86 Sr in fluorite and fluorite-host granites show that fluorite records the differentiation trend of the host Tabuleiro granites. REE-normalized patterns and Eu/Eu* relations in fluorite-bearing granites indicate that fluorite forms after the crystallization of the quartzo-feldspathic framework in residual melts. The Tabuleiro accessory fluorites yield high and variable 87 Sr/ 86 Sr ratios between 0.72334 and 0.8192. These ratios are neither the result of fluorite precipitation from a fluid nor Sr isotopic resetting. They result from 87 Rb decay in fluorine-rich high-Rb/Sr melts evolved by fractional crystallization in a magmatic system with a long crystallization time-span. Melt residence times of 300 to 700 ka and D Sr of 4.7 to 6.0 are necessary to yield the high fluorite 87 Sr/ 86 Sr ratios. These results are compatible with those deduced elsewhere from high-silica rhyolitic volcanic equivalents.

Synthetic Fluid Inclusions XIV: Coexisting Silicate Melt and Aqueous Fluid Inclusions in the Haplogranite-H2O-NaCl-KCl System

Coeval silicate melt and aqueous synthetic fluid inclusions were INTRODUCTION formed at 800°C and 2000 bars in the quartz-saturated haploIn recent years the study of silicate melt inclusions has granite–H2O–NaCl–KCl system. The equilibrium assemblage congained considerable popularity as a method to charsisted of Ab19·2Or31·1Qtz49·1 melt, quartz, and an aqueous solution acterize the PTX evolution of igneous processes (Andwith a composition of 7·4 wt % NaCl + 5·9 wt % KCl. The erson, 1974; Roedder, 1979; Lowenstern, 1995). Of melt contained 0·18 wt % Cl – and ~5·5 wt % H2O. The special interest has been the study of melt inclusions calculated partition coefficient of chloride between the melt and trapped in an immiscible fluid–melt system (Roedder, aqueous fluid (D m/aq Cl =C m Cl/C aq Cl ) is 0·021. The calculated dis1979, 1984, 1992; Hansteen & Lustenhouwer, 1990; tribution coefficient of Na and K between the melt and the aqueous Frezzotti, 1992; Naumov et al., 1992, 1996; Yang & phase D m/aq Na/K=(C m Na/C m K )/(C aq Na/C aq K )) is 0·40. Homogenization Bodnar, 1994; Student & Bodnar, 1996). Microtemperatures of synthetic silicate melt inclusions obtained by heating thermometric data from such inclusions can be used in 10·0°C/day increments in a tube furnace agreed with known directly to determine formation temperatures and presformation temperatures, with no size dependence. When measured sures, without the necessity of invoking difficult to prove in a high-temperature heating stage, a heating rate of 1°C/min assumptions or requiring an independent geobarometer produced homogenization temperatures that were about 10°C lower or geothermometer (Roedder & Bodnar, 1980). than those obtained from the same inclusions using a heating rate Roedder (1992) described specific types of magmatic of 3°C/min, although both heating rates produced homogenization immiscibility (immiscibility being defined as the existence temperatures above the formation temperature. A positive correlation of two or more non-crystalline, multi-component sobetween inclusion size and Th was observed for both heating rates. lutions which differ in properties and composition at Results confirm that microthermometric data from coeval silicate equilibrium), including silicate melt–silicate melt, silicate melt and aqueous fluid inclusions can be used to accurately predict melt–sulfide melt and silicate melt–aqueous fluid. In this P–T formation conditions if data from the smallest melt inclusions study we have investigated the behavior of synthetic fluid are used, or if the melt inclusions are homogenized using a slow inclusions trapped under conditions of silicate melt– heating rate (<1°C/min). aqueous fluid immiscibility in the haplogranite–

Suppression of channel convection in solidifying Pb-Sn alloys via an applied magnetic field

Channel convection through the porous, dendritic mushy zone in solidifying alloys results from a nonlinear focusing mechanism, whereby liquid enriched in the solute melts dendrites as it convects away from the solid. The local melting reduces the parameterized (Darcy) viscous force and increases the flow speed to form a convective channel. However, it has been predicted that an applied magnetic field might prevent channels from forming because, as the Lorentz force replaces the Darcy force as the primary resistance to flow, the retarding force becomes less sensitive to the lengthscale of the flow, so that the focusing mechanism no longer operates. In this study, it is found experimentally that, as predicted, an applied horizontal magnetic field can suppress channel convection when Q m , the Chandrasekhar number appropriate to a mushy zone, exceeds an order of one. The nondimensional number Q m is a measure of the strength of the Lorentz force relative to the Darcy force in the mushy zone and, for a given magnetic field, is much smaller than the analogous Chandrasekhar number (Q) for the fluid melt, since the Darcy force in the mushy zone far exceeds the viscous force in the fluid. Previous experimental work failed to find that magnetic fields could suppress channel convection because, although Q exceeded an order of one, Q m did not. For experiments with a smaller cooling rate, and, thus, a larger permeability and larger mushy zone Rayleigh number (Ra m ) a stronger magnetic field is necessary to suppress channel convection. The longitudinal macrosegregation is not affected by the absence of channel convection, suggesting that such channels are not always primarily responsible for the mass flux between the mushy zone and the melt.

Dehydration and cold hardiness in the Arctic Collembolan Onychiurus arcticus Tullberg 1876

Specimens of the Arctic Collembolon Onychiurus arcticus were exposed to desiccation at several subzero temperatures over ice and at 0.5 °C over NaCl solutions. The effects of desiccation on water content (WC), body fluid melting point (MP), supercooling point (SCP) and survival were studied at several acclimation temperatures and relative humidities. Exposure to temperatures down to −19.5 °C caused a substantial and increasing dehydration. At the lowest exposure temperature unfrozen individuals lost 91.6% of the WC at full hydration but more than 80% of the individuals survived when rehydrated. Exposure at 0.5 °C to decreasing relative humidities (RH) from 100% to 91.3% caused increasing dehydration and increasing mortality. Survival of equally dehydrated individuals was higher at subzero temperatures than at 0.5 °C. Concurrent with the decline in WC a lowering of the MP was observed. Animals exposed to −3 °C and −6 °C over ice for 31 days had a MP of −3.8 and < −7.5 °C, respectively. Specimens from a laboratory culture had a mean SCP of −6.1 °C, and acclimation at 0 or −3 °C had little effect on SCPs. Exposure at −8.2 °C over ice for 8 days, however, caused the mean SCP to decline to −21.8 °C due to the severe dehydration of these individuals. Dehydration at 0.5 °C in 95.1 and 93.3% RH also caused a decline in SCPs to about −18 °C. Individuals that had been acclimated over ice at −12.4 °C or at lower temperatures apparently did not freeze at all when cooled to −30 °C, probably because all freezeable water had been lost. These results show that O. arcticus will inevitably undergo dehydration when exposed to subzero temperatures in its natural frozen habitat. Consequently, the MP and SCP of the Collembola are substantially lowered and in this way freezing is avoided. The increased cold hardiness by dehydration is similar to the protective dehydration mechanism described in earthworm cocoons and Arctic enchytraeids.

Isotopic and trace element constraints on the genesis of a boninitic sequence in the Thetford Mines ophiolitic complex, Quebec, Canada

The Mont Ham Massif (part of the Thetford Mines ophiolite, south Quebec) represents a magmatic sequence made up of tholeiitic and boninitic derived products. A geochemical study confirms the multicomponent mixing models that have been classically advanced for the source of boninites, with slab-derived components added to the main refractory harzburgitic peridotite. An isochron diagram of the boninitic rocks is interpreted as a mixing trend between two components: (i) a light rare earth element (LREE) enriched component (A), interpreted as slab-derived fluid–melts equilibrated with sedimentary materials (εNd = −3, 147Sm/144Nd = 0.140), and (ii) a LREE-depleted component (B) (0.21 &lt; 147Sm/144Nd &lt; 0.23), interpreted as slab-derived fluid–melt equilibrated with recycled Iapetus oceanic crust and equated to the Nd-isotope characteristics of the Iapetus mantle (εNd = 9). A multicomponent source is also necessary to explain the Nd-isotope and trace element composition of the tholeiites, which are explained by the melting of a more fertile, lherzolitic mantle and (or) mid-ocean ridge basalt source (component C), characterized by a large-ion lithophile element depleted pattern and an Iapetus mantle Nd isotopic composition (εNd = 9), mixed in adequate proportions with the two previously infered slab-derived components (A and B). The genesis of the boninites of Mont Ham is not significantly different from those of boninites located in the Pacific. An intraoceanic subduction zone appears to be an appropriate geodynamic environment for the Mont Ham ophiolitic sequence.

Directional solidification into static stability

Consider the directional solidification of a binary alloy rejecting a heavy solute as it solidifies upward. If the solidification front is planar, the fluid melt ahead of the front is stably stratified and convection is not expected. In this paper we analyse the linear stability of planar solidification asymptotically in the limit of large solutal Rayleigh number, R. Three distinct linear modes are found which correspond to internal waves, buoyancy edge waves, or morphological modes. Of these three modes, only the morphological modes are subject to an instability. We find that for large Rayleigh number this instability first occurs at long wavelengths with wavenumbers that scale on R−1/14. The scalings derived from the linear analysis are used to construct a nonlinear theory for the morphological instability in the large Rayleigh number limit. Similarity solutions are found which describe steadily convecting, non-planar growth reminiscent of an observed phenomenon known as steepling.