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Sample records for silicate melt pockets

  1. Unusual Siderite-Bearing Dendrites in Melt Pockets of the Elga IIE Iron

    NASA Astrophysics Data System (ADS)

    Teplyakova, S. N.; Artemov, V. V.; Vasiliev, A. L.

    2012-03-01

    The Elga iron contains melt pockets with dedritic texture not only inside Fe,Ni-metal but also inside silicate inclusions (SI). The unusual siderite-bearing melt pockets inside SIs has never been previously observed in any types of meteorites.

  2. Molybdenum Valence in Basaltic Silicate Melts

    NASA Technical Reports Server (NTRS)

    Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Pando, K.

    2010-01-01

    The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

  3. Dynamic crystallization of silicate melts

    NASA Technical Reports Server (NTRS)

    Russell, W. J.

    1984-01-01

    Two types of furnaces with differing temperature range capabilities were used to provide variations in melt temperatures and cooling rates in a study of the effects of heterogeneous nucleation on crystallization. Materials of chondrule composition were used to further understanding of how the disequilibrium features displayed by minerals in rocks are formed. Results show that the textures of natural chondrules were duplicated. It is concluded that the melt history is dominant over cooling rate and composition in controlling texture. The importance of nuclei, which are most readily derived from preexisting crystalline material, support an origin for natural chondrules based on remelting of crystalline material. This would be compatible with a simple, uniform chondrule forming process having only slight variations in thermal histories resulting in the wide range of textures.

  4. Electrical conductivity measurements on silicate melts using the loop technique

    NASA Technical Reports Server (NTRS)

    Waff, H. S.

    1976-01-01

    A new method is described for measurement of the electrical conductivity of silicate melts under controlled oxygen partial pressure at temperatures to 1550 C. The melt samples are suspended as droplets on platinum-rhodium loops, minimizing iron loss from the melt due to alloying with platinum, and providing maximum surface exposure of the melt to the oxygen-buffering gas atmosphere. The latter provides extremely rapid equilibration of the melt with the imposed oxygen partial pressure. The loop technique involves a minimum of setup time and cost, provides reproducible results to within + or - 5% and is well suited to electrical conductivity studies on silicate melts containing redox cations.

  5. Silicate-melt inclusions in magmatic rocks: applications to petrology

    NASA Astrophysics Data System (ADS)

    Frezzotti, Maria-Luce

    2001-01-01

    Silicate-melt inclusions in igneous rocks provide important information on the composition and evolution of magmatic systems. Such inclusions represent accidentally trapped silicate melt (±immiscible H 2O and/or CO 2 fluids) that allow one to follow the evolution of magmas through snapshots, corresponding to specific evolution steps. This information is available on condition that they remained isolated from the enclosing magma after their entrapment. The following steps of investigation are discussed: (a) detailed petrographic studies to characterise silicate-melt inclusion primary characters and posttrapping evolution, including melt crystallisation; (b) high temperature studies to rehomogenise the inclusion content and select chemically representative inclusions: chemical compositions should be compared to relevant phase diagrams. Silicate-melt inclusion studies allow us to concentrate on specific topics; inclusion studies in early crystallising phases allow the characterisation of primary magmas, while in more differentiated rocks, they unravel the subsequent chemical evolution. The distribution of volatile species (i.e., H 2O, CO 2, S, Cl) in inclusion glass can provide information on the degassing processes and on recycling of subducted material. In intrusive rocks, silicate melt inclusions may preserve direct evidence of magmatic stage evolution (e.g., immiscibility phenomena). Melt inclusions in mantle xenoliths indicate that high-silica melts can coexist with mantle peridotites and give information on the presence of carbonate melt within the upper mantle. Thus, combining silicate-melt inclusion data with conventional petrological and geochemical information and experimental petrology can increase our ability to model magmatic processes.

  6. Mantle Mineral/Silicate Melt Partitioning

    NASA Astrophysics Data System (ADS)

    McFarlane, E. A.; Drake, M. J.

    1992-07-01

    Introduction: The partitioning of elements among mantle phases and silicate melts is of interest in unraveling the early thermal history of the Earth. It has been proposed that the elevated Mg/Si ratio of the upper mantle of the Earth is a consequence of the flotation of olivine into the upper mantle (Agee and Walker, 1988). Agee and Walker (1988) have generated a model via mass balance by assuming average mineral compositions to generate upper mantle peridotite. This model determines that upper mantle peridotite could result from the addition of 32.7% olivine and 0.9% majorite garnet into the upper mantle, and subtraction of 27.6% perovskite from the upper mantle (Agee and Walker, 1988). The present contribution uses experimental data to examine the consequences of such multiple phase fractionations enabling an independent evaluation of the above mentioned model. Here we use Mg-perovskite/melt partition coefficients from both a synthetic and a natural system (KLB-1) obtained from this laboratory. Also used are partition coefficient values for majorite garnet/melt, beta spinel/melt and olivine/melt partitioning (McFarlane et al., 1991b; McFarlane et al., 1992). Multiple phase fractionations are examined using the equilibrium crystallization equation and partition coefficient values. The mineral proportions determined by Agee and Walker (1988) are converted into weight fractions and used to compute a bulk partition coefficient value. Discussion: There has been a significant debate concerning whether measured values of trace element partition coefficients permit large-scale fractionation of liquidus phases from an early terrestrial magma ocean (Kato et al., 1988a,b; Walker and Agee, 1989; Drake, 1989; Drake et al., 1991; McFarlane et al., 1990, 1991). It should be noted that it is unclear which, if any, numerical values of partition coefficients are appropriate for examining this question, and certainly the assumptions for the current model must be more fully

  7. Experimental study of the electrolysis of silicate melts

    NASA Technical Reports Server (NTRS)

    Keller, R.; Larimer, K. T.

    1991-01-01

    To produce oxygen from lunar resources, it may be feasible to melt and electrolyze local silicate ores. This possibility was explored experimentally with synthesized melts of appropriate compositions. Platinum electrodes were employed at a melt temperature of 1425 C. When silicon components of the melt were reduced, the platinum cathode degraded rapidly, which prompted the substitution of a graphite cathode substrate. Discrete particles containing iron or titanium were found in the solidified electrolyte after three hours of electrolysis. Electrolyte conductivities did not decrease substantially, but the escape of gas bubbles, in some cases, appeared to be hindered by high viscosity of the melt.

  8. Conductimetric determination of decomposition of silicate melts

    NASA Technical Reports Server (NTRS)

    Kroeger, C.; Lieck, K.

    1986-01-01

    A description of a procedure is given to detect decomposition of silicate systems in the liquid state by conductivity measurements. Onset of decomposition can be determined from the temperature curves of resistances measured on two pairs of electrodes, one above the other. Degree of decomposition can be estimated from temperature and concentration dependency of conductivity of phase boundaries. This procedure was tested with systems PbO-B2O3 and PbO-B2O3-SiO2.

  9. Activity composition relationships in silicate melts

    SciTech Connect

    Glazner, A.F.

    1990-01-01

    Equipment progress include furnace construction and electron microprobe installation. The following studies are underway: phase equilibria along basalt-rhyolite mixing line (olivine crystallization from natural silicic andensites, distribution of Fe and Mg between olivine and liquid, dist. of Ca and Na between plagioclase and liquid), enthalpy-composition relations in magmas (bulk heat capacity of alkali basalt), density model for magma ascent and contamination, thermobarometry in igneous systems (olivine/plagioclase phenocryst growth in Quat. basalt), high-pressure phase equilibria of alkali basalt, basalt-quartz mixing experiments, phase equilibria of East African basalts, and granitic minerals in mafic magma. (DLC)

  10. Formation of iron melt channels in silicate perovskite at Earth's lower mantle conditions

    NASA Astrophysics Data System (ADS)

    Shi, C. Y.; Liu, Y.; Wang, J.; Zhang, L.; Yang, W.; Mao, W. L.

    2012-12-01

    Core-formation represents the most significant differentiation event in Earth's history. Earth's current layered structure with a metallic core and an overlying silicate mantle requires mechanism(s) to separate the iron alloy from the silicates in the initially accreted material. Many mechanisms have been proposed. At upper mantle conditions, percolation was ruled out as an efficient mechanism due to the tendency of liquid iron alloy to form isolated pockets at these pressures and temperatures. We investigated the ability of a liquid iron alloy to form an interconnected melt network with (Mg,Fe)SiO3 perovskite (pv) under Earth's lower mantle conditions using a laser-heated diamond-anvil cell (DAC). Using nanoscale synchrotron X-ray computed tomography, we imaged a dramatic change in the shape of the iron-rich melt in the three-dimensional (3D) reconstructions of samples prepared at varying pressures and temperatures. We found that the iron distribution went from isolated pockets to an interconnected network as the pressure increased.

  11. Sulfur Solubility In Silicate Melts: A Thermochemical Model

    NASA Astrophysics Data System (ADS)

    Moretti, R.; Ottonello, G.

    A termochemical model for calculating sulfur solubility of simple and complex silicate melts has been developed in the framework of the Toop-Samis polymeric approach combined with a Flood - Grjotheim theoretical treatment of silicate slags [1,2]. The model allows one to compute sulfide and sulfate content of silicate melts whenever fugacity of gaseous sulphur is provided. "Electrically equivalent ion fractions" are needed to weigh the contribution of the various disproportion reactions of the type: MOmelt + 1/2S2 ,gas MSmelt+1/2O2 ,gas (1) MOmelt + 1/2S2 ,gas + 3/2O2 ,gas MSO4 ,melt (2) Eqs. 1 and 2 account for the oxide-sulfide and the oxide-sulfate disproportiona- tion in silicate melt. Electrically equivalent ion fractions are computed, in a fused salt Temkin notation, over the appropriate matrixes (anionic and cationic). The extension of such matrixes is calculated in the framework of a polymeric model previously developed [1,2,3] and based on a parameterization of acid-base properties of melts. No adjustable parameters are used and model activities follow the raoultian behavior implicit in the ion matrix solution of the Temkin notation. The model is based on a huge amount of data available in literature and displays a high heuristic capability with virtually no compositional limits, as long as the structural role assigned to each oxide holds. REFERENCES: [1] Ottonello G., Moretti R., Marini L. and Vetuschi Zuccolini M. (2001), Chem. Geol., 174, 157-179. [2] Moretti R. (2002) PhD Thesis, University of Pisa. [3] Ottonello G. (2001) J. Non-Cryst. Solids, 282, 72-85.

  12. Osmium Solubility in Silicate Melts: New Efforts and New Results

    NASA Technical Reports Server (NTRS)

    Borisov, A.; Walker, R. J.

    1998-01-01

    In a recent paper, Borisov and Palme reported the first experimental results on the partitioning of Os between metal (Ni-rich OsNi alloys) and silicate melt of anorthite-diopside eutectic composition at 1400 C and 1 atm total pressure and and at function of O2 from 10(exp -8) to 10(exp -12) atm. Experiments were done by equilibrating OsNi metal loops with silicate melt. Metal and glass were analyzed separately by INAA. D(sup 0s) ranged from 10(exp 6) to 10(exp 7), which is inconsistent with core/ mantle equilibrium for HSEs and favors the late veneer hypothesis. Unfortunately, there was practically no function of O2 dependence of Os partitioning, and the scatter of experimental results was quite serious, so the formation of Os nuggets was suspected. This new set of experiments was specifically designed to avoid of at least minimize the nugget problem

  13. Experimental study of chlorine behavior in hydrous silicic melts

    SciTech Connect

    Metrich, N. ); Rutherford, M.J. )

    1992-02-01

    Chlorine solubility in silicate melts has been investigated at 830-850 {plus minus} 5C and at pressures ranging from 50 to 200 MPa, using both natural (pantellerite, rhyolite, phonolite) and synthetic (SiO{sub 2}-Al{sub 2}O{sub 3}-K{sub 2}O-Na{sub 2}O) compositions and a stated H{sub 2}O-NaCl-KCl fluid phase near 4 molal. At 100 MPa, Cl contents in pantelleritic melts reach a solubility plateau at initial aqueous phase molality near 2. This plateau coincides with a large immiscibility gap between aqueous and chloride-rich fluids. With the coexisting Cl-saturated aqueous phase, Cl ranges from 2,720 {plus minus} 120 ppm in rhyolite to 8,960 {plus minus} 85 ppm in pantellerite and reaches 6,270 {plus minus} 170 ppm in phonolite, at 100 MPa. Between 50 and 200 MPa, the Cl content in pantelleritic melt decreases from 9,640 {plus minus} 200 ppm to 5,040 {plus minus} 150 ppm. Although Cl solubility increases with increasing FeO{sup *} in high SiO{sub 2} melts, it is mainly controlled by the Al/Si and (Na + K)/Al molar ratios of the melt with a minimum at Na + K/Al = 1 in a series of synthetic rhyolitic to pantelleritic melts. The experimental results suggest that chlorine occurs as alkali-chloride complexes in high SiO{sub 2} melts. They also indicate that Cl is concentrated in the aqueous fluids in equilibrium with SiO{sub 2}-rich melts, the exact value of D depending on melt composition and melt chlorine concentration. Volcanic degassing will create chlorine-rich hydrothermal fluids and decrease chlorine melt content.

  14. The speciation of carbon dioxide in silicate melts

    NASA Astrophysics Data System (ADS)

    Konschak, Alexander; Keppler, Hans

    2014-05-01

    The speciation of CO2 in dacite, phonolite, basaltic andesite, and alkali silicate melt was studied by synchrotron infrared spectroscopy in diamond anvil cells to 1,000 °C and more than 200 kbar. Upon compression to 110 kbar at room temperature, a conversion of molecular CO2 into a metastable carbonate species was observed for dacite and phonolite glass. Upon heating under high pressure, molecular CO2 re-appeared. Infrared extinction coefficients of both carbonate and molecular CO2 decrease with temperature. This effect can be quantitatively modeled as the result of a reduced occupancy of the vibrational ground state. In alkali silicate (NBO/ t = 0.98) and basaltic andesite (NBO/ t = 0.42) melt, only carbonate was detected up to the highest temperatures studied. For dacite (NBO/ t = 0.09) and phonolite melts (NBO/ t = 0.14), the equilibrium CO2 + O2- = CO3 2- in the melt shifts toward CO2 with increasing temperature, with ln K = -4.57 (±1.68) + 5.05 (±1.44) 103 T -1 for dacite melt (Δ H = -42 kJ mol-1) and ln K = -6.13 (±2.41) + 7.82 (±2.41) 103 T -1 for phonolite melt (Δ H = -65 kJ mol-1), where K is the molar ratio of carbonate over molecular CO2 and T is temperature in Kelvin. Together with published data from annealing experiments, these results suggest that Δ S and Δ H are linear functions of NBO/ t. Based on this relationship, a general model for CO2 speciation in silicate melts is developed, with ln K = a + b/ T, where T is temperature in Kelvin and a = -2.69 - 21.38 (NBO/ t), b = 1,480 + 38,810 (NBO/ t). The model shows that at temperatures around 1,500 °C, even depolymerized melts such as basalt contain appreciable amounts of molecular CO2, and therefore, the diffusion coefficient of CO2 is only slightly dependent on composition at such high temperatures. However, at temperatures close to 1,000 °C, the model predicts a much stronger dependence of CO2 solubility and speciation on melt composition, in accordance with available solubility data.

  15. Mg-perovskite/silicate melt and magnesiowuestite/silicate melt partition coefficients for KLB-1 at 250 Kbars

    NASA Technical Reports Server (NTRS)

    Drake, Michael J.; Rubie, David C.; Mcfarlane, Elisabeth A.

    1992-01-01

    The partitioning of elements amongst lower mantle phases and silicate melts is of interest in unraveling the early thermal history of the Earth. Because of the technical difficulty in carrying out such measurements, only one direct set of measurements was reported previously, and these results as well as interpretations based on them have generated controversy. Here we report what are to our knowledge only the second set of directly measured trace element partition coefficients for a natural system (KLB-1).

  16. Lunar highland melt rocks - Chemistry, petrology and silicate mineralogy

    NASA Technical Reports Server (NTRS)

    Vaniman, D. T.; Papike, J. J.

    1980-01-01

    A selected suite containing several of the largest samples of lunar highland melt rocks includes impact melt specimens (anorthositic gabbro, low-K Fra Mauro) and volcanic specimens (intermediate-K Fra Mauro). Although previous assumptions of LKFM volcanism have fallen into disfavor, no fatal arguments against this hypothesis have been presented, and the evidence of a possibly 'inherited igneous' olivine-plagioclase cosaturation provides cause for keeping a volcanic LKFM hypothesis viable. Comparisons of silicate mineralogy with melt rock compositions provide information on the specimen's composition and cooling history. Plagioclase-rock compositions can be matched to the experimentally determined equilibria for appropriate samples to identify melt rocks with refractory anorthitic clasts. Olivine-rock compositions indicate that melt rock vitrophyres precipitate anomalously Fe-rich olivine; the cause of this anomaly is not immediately evident. The Al-Ti and Ca-Fe-Mg zonation in pyroxene provide information on relative cooling rates of highland melt rocks, but Cr- and Al-content (where Al-rich low-Ca pyroxene cores are preserved in rapidly cooled samples) can be correlated with composition of the host rock.

  17. (Energetics of silicate melts from thermal diffusion studies)

    SciTech Connect

    Not Available

    1990-01-01

    The first year of this three year renewal award has been used to continue data collection and analysis of thermal (Soret) diffusion in silicate liquid and explore the related process of thermal migration in subliquidus magmas and isothermal interdiffusion. Data collection efforts have been materially aided by advances in thermal insulation in the pressure media outside our pressurized cylindrical heaters. BaCO{sub 3} is very effective in protecting the pressure vessel core from thermal deterioration with the result that the heater inside and outside diameters can be substantially increased. This permits several charges to be run simultaneously in an axisymmetric cluster around a double or triple junction thermocouple which can measure axial thermal gradients in situ. Research during the past year has concentrated in four major areas: Modelling thermal diffusion in multi-component silicate liquids, Soret fractionation of major and minor chemical components, characterization of thermal diffusion in naturally-occurring magmas with an emphasis on volatile bearing rhyolitic melts, and the effects of thermal gradients on silicate magma in the melting interval.

  18. The mechanisms of water diffusion in polymerized silicate melts

    NASA Astrophysics Data System (ADS)

    Behrens, Harald; Nowak, M.

    1997-02-01

    Diffusion of water was experimentally investigated for melts of albitic (Ab) and quartz-orthoclasic (Qz29Or71, in wt %) compositions with water contents in the range of 0 to 8.5 wt % at temperatures of 1100 to 1200 °C and at pressures of 1.0 and 5.0 kbar. Apparent chemical diffusion coefficients of water ( D water) were determined from concentration-distance profiles measured by FTIR microspectroscopy. Under the same P- T condition and water content the diffusivity of water in albitic, quartz-orthoclasic and haplogranitic (Qz28Ab38 Or34, Nowak and Behrens, this issue) melts is identical within experimental error. Comparison to data published in literature indicates that anhydrous composition only has little influence on the mobility of water in polymerized melts but that the degree of polymerization has a large effect. For instance, Dwater is almost identical for haplogranitic and rhyolitic melts with 0.5-3.5 wt % water at 850 °C but it is two orders of magnitude higher in basaltic than in haplogranitic melts with 0.2-0.5 wt % water at 1300 °C. Based on the new water diffusivity data, recently published in situ near-infrared spectroscopic data (Nowak 1995; Nowak and Behrens 1995), and viscosity data (Schulze et al. 1996) for hydrous haplogranitic melts current models for water diffusion in silicate melts are critically reviewed. The NIR spectroscopy has indicated isolated OH groups, pairs of OH groups and H2O molecules as hydrous species in polymerized silicate melts. A significant contribution of isolated OH groups to the transport of water is excluded for water contents above 10 ppm by comparison of viscosity and water diffusion data and by inspection of concentration profiles from trace water diffusion. Spectroscopic measurements have indicated that the interconversion of H2O molecules and OH pairs is relatively fast in silicate glasses and melts even at low temperature and it is inferred that this reaction is an active step for migration of water. However

  19. The solubility of gold in silicate melts: First results

    NASA Technical Reports Server (NTRS)

    Borisov, A.; Palme, H.; Spettel, B.

    1993-01-01

    The effects of oxygen fugacity and temperature on the solubility of Au in silicate melts were determined. Pd-Au alloys were equilibrated with silicate of anorthite-diopside eutectic composition at different T-fO2 conditions. The behavior of Au was found to be similar to that of Pd reported recently. Au solubilities for alloys with 30 to 40 at. percent Au decrease at 1400 C from 12 ppm in air to 160 ppb at a log fO2 = -8.7. The slope of the log(Me-solubility) vs. log(fO2) curve is close to 1/4 for Au and the simultaneously determined Pd suggesting a formal valence of Au and Pd of 1+. Near the IW buffer Pd and Au solubilities become even less dependent on fO2 perhaps reflecting the presence of some metallic Au and Pd.

  20. Nitrogen Partitioning Between Reduced Silicate Melts and Metallic Iron Alloys

    NASA Astrophysics Data System (ADS)

    Armstrong, L. S.; Falksen, E.; Von Der Handt, A.; Hirschmann, M. M.

    2014-12-01

    Solubility and partitioning of elements during early planetary history is critical in understanding element concentrations and distribution in the terrestrial planets. Nitrogen is the most depleted element in the bulk silicate Earth relative to CI chondrites [1], which may be explained by its high pressure behavior under reduced conditions relevant to planetary accretion and differentiation. Under oxidized conditions N dissolves in silicate melts as N2, but as fO2 decreases N-H species become the dominant form of dissolved N and the solubility increases [2-7]. DNmetal/melt (the N partition coefficient between metal and melt) is affected by pressure, fO2, fH2, and metal composition [3-5] but with less than 20 published experiments over a wide pressure range, these dependencies have been poorly constrained. Here we present new N-bearing experiments on graphite-saturated silicate melts in equilibrium with Fe-rich metallic melts. Experiments were performed at 1.2 GPa and 1400 ˚C in a piston cylinder apparatus, with N added as Si3N4, FexN, and urea [(NH2)2CO] to basaltic starting compositions. Glassy and metallic run products were gold coated and analyzed by EMPA. Detection limits and standard errors in N concentrations were improved (e.g. better than 1% for > 0.4 wt% N) relative to previous studies [2-5] by fitting non-linear backgrounds to wavelength-scans on standards and unknowns. Preliminary experiments with fO2 of IW-2 to IW-4 produced glasses with a maximum of 0.6 wt% N and metals with a maximum of 1.1 wt% N. DNmetal/melt are comparable to values at a similar pressure determined in the LH-DAC [5]. Further experiments will explore the effects of fO2 and H content on DN and N solubility. References: [1] Halliday (2013) GCA 105, 146-171. [2] Libourel et al. (2003) GCA 67, 4123-4135. [3] Kadik et al. (2011) Geochem. Int. 49, 429-438. [4] Kadik et al. (2013) PEPI 214, 14-24. [5] Roskosz et al. (2013) GCA 121, 15-28. [6] Stanley et al. (2014) GCA 129, 54-76. [7

  1. Copper and molybdenum in silicate melt-aqueous fluid systems

    SciTech Connect

    Candela, P.A.

    1982-01-01

    The partitioning of copper (Cu) and molybdenum (Mo) between silicate melts and aqueous fluids has been determined. The vapor/melt partition coefficient for Cu, D(Cu) was found to be D(Cu) = 9.2 m/sub Cl//sup v/ at NNO. The partition coefficient for Mo, D(Mo), is equal to 2.5 at NNO and QFM, and is independent of the F and Cl concentration. Equations have been derived for the efficiency of the removal of the metals from magmas into aqueous fluids. Copper is concentrated so efficiently into a moderately to highly saline aqueous phase that liquid-vapor extraction seems to be a reasonable process to account for the concentration of Cu in porphyry Cu deposits. However, geological evidence suggests that Cu behaves as a compatible element during magmatic processes(BPC > 1). Therefore, the efficiency of Cu removal from magmas into aqueous fluids is strongly dependent upon the amount of the melt crystallized before water saturation, and efficient extraction of Cu results when aqueous fluids are evolved early in the crystallization of the intrusion. The value of D(Mo) is small relative to D(Cu) at moderate to high chloride concentrations, and the extraction of Mo from melts into aqueous fluids therefore tends to be less efficient. However, vapor-liquid partitioning can extract the requisite quantities of Mo from granitic melts of batholithic size.

  2. Experimental study of the electrolysis of silicate melts

    NASA Technical Reports Server (NTRS)

    Keller, Rudolf

    1992-01-01

    Melting and electrolyzing lunar silicates yields oxygen gas and potentially can be practiced in situ to produce oxygen. With the present experiments conducted with simulant oxides at 1425-1480 C, it was ascertained that oxygen can be obtained anodically at feasible rates and current efficiencies. An electrolysis cell was operated with platinum anodes in a sealed vessel, and the production of gas was monitored. In these electrolysis experiments, stability of anodes remained a problem, and iron and silicon did not reduce readily into the liquid silver cathode.

  3. Spherulite Crystallization Induces Fe-Redox Redistribution in Silicic Melt

    SciTech Connect

    Castro, J.; Cottrell, E; Tuffen, H; Logan, A; Kelley, K

    2009-01-01

    Rhyolitic obsidians from Krafla volcano, Iceland, record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt. We performed synchrotron {mu}-FTIR and {mu}-XANES measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones. Measurements show that the colorless glass is enriched in OH groups and depleted in ferric iron, while the brown glass shows the opposite relationship. The color shift between brown and clear glass is sharp, suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization. We conclude that the most likely reducing agent is hydrogen, produced by magnetite crystallization within the spherulite. The Krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late-stage crystallization to the redox signature of glassy lavas.

  4. Experimental determination of the solubility of iridium in silicate melts: Preliminary results

    NASA Technical Reports Server (NTRS)

    Borisov, Alexander; Dingwell, Donald B.; Oneill, Hugh ST.C.; Palme, Herbert

    1992-01-01

    Little is known of the geochemical behavior of iridium. Normally this element is taken to be chalcophile and/or siderophile so that during planetary differentiation processes, e.g., core formation, iridium is extracted from silicate phases into metallic phases. Experimental determination of the metal/silicate partition coefficient of iridium is difficult simply because it is so large. Also there are no data on the solubility behavior of iridium in silicate melts. With information on the solubility of iridium in silicate melts it is possible, in combination with experimental data for Fe-Ir alloys, to calculate the partition coefficient between a metallic phase and a silicate melt.

  5. The limitations of melting on the reactivation of silicic mushes

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Bachmann, Olivier; Dufek, Josef

    2010-08-01

    High crystallinity silicic ignimbrites (such as the Monotonous Intermediates) typically erupt magma with an average crystallinity ranging from 40 to 50%. This average crystallinity is believed to be just under the threshold at which magma behaves as a solid (50-60% crystals), i.e. the locking point crystallinity, where convection is suppressed and large eruptions are unlikely. These magmas often display textural features which suggest that their average crystallinity was once higher and decreased before the eruption as a result of reheating through the injection of new magma. In this study, we use a theoretical 1D heat conduction model with phase change to test the ability of different melting scenarios of crystal mushes to meet the 40 to 50% crystallinity constraint observed in the field. Our heat conduction and melting models allow us to derive analytical solutions for the average crystallinity in the magma body (initially a crystal mush). We focus on the propagation of the melting front coinciding with the locking point crystallinity for different crystallinity-temperature relationships and various choices of temperature boundary conditions. We develop another analytical model based on stagnant-lid convection scaling to assess the role of convection on the expected average crystallinity of the magma subjected to wholesale steady-state convection. We find that, for all realistic melting scenarios, the average crystallinity of a silicic magma body that passed through the rheological transition is always substantially lower than what is observed in the field. We further show with a simple energy balance that the thermal energy needed to unlock/remobilize these magma bodies requires the intrusion of about an order of magnitude of more magma than the mush. Based on these results we argue that, although melting is a key process in the thermal reactivation of high crystallinity magma bodies, another coupled process is required in order to reactivate large volumes of

  6. Visualizing microscopic structure and dynamics of simulated silicate melts

    NASA Astrophysics Data System (ADS)

    Karki, B. B.; Bohara, B.

    2013-12-01

    We perform a detailed visualization-based analysis of atomic-position series data for silicate melts obtained from first-principles (quantum mechanical) molecular dynamics simulations. This involves processing atomic trajectories as well as relevant structural and dynamical information. Clutter associated with trajectory rendering can be reduced with an adaptive position-merging scheme. To gain insight into the short- and mid-range order of the melt structure, we extract and visualize the details of radial distribution function (RDF) and coordination environment. The first peaks of all partial RDFs lie in the distance range of 1.6 to 4 Å and the corresponding mean coordination numbers vary from less than 1 to more than 9. The coordination environments involving cations and anions differ substantially from each other, each consisting of a rich set of coordination states. These states vary both spatially and temporally: The per-atom coordination information extracted on the fly is rendered instantaneously as the spheres and polyhedra as well as along the corresponding trajectories using a color-coding scheme. The information is also visualized as clusters formed by atoms that are coordinated at different time intervals during the entire simulation. The animated visualization suggests that the melt structure can be viewed as a dynamic (partial) network of Al/Si-O coordination polyhedra connected via bridging oxygen in an inhomogeneous distribution of mobile cations including magnesium, calcium, and protons.

  7. Structural study of nickel reduction in silicate melts

    NASA Astrophysics Data System (ADS)

    Marcq, B.; Galoisy, L.; Libourel, G.; Calas, G.

    2003-04-01

    Composition of the global Earth has been partially controlled by precursors chemical variability (chondrites) and by primitive earth differentiation processes. In the core, the segregation of a metallic phase (Fe, Ni) and the metal-silicate melt reactions are essential to understand primitive earth differenciation processes. From an industrial point of view, the segregation of a metallic phase from melts is widely used in metallurgy to obtain steel and cast in blast furnaces. Ni2+ bearing glasses, used as snapshot of the corresponding, melts have been synthesized under a controlled oxygen fugacity, in order to understand metal-silicate melts reduction mechanisms. The aim of this study is to follow Ni2+ environment, as a function of reduction. The methods used, optical absorption spectroscopy, EXAFS and XANES, precisely describe the sites occupied by Ni2+ in the glass. Reduction experiments were performed between 1350^oC and 1365^oC using a composition close to the anorthite-diopside system eutectic (49% SiO_2, 22% CaO, 19% Al_2O_3, 9% MgO in weight percent) with 1% NiO. A wide range of oxygen fugacities has been used, from 6.5 (Ni +1/2 O_2 <-> NiO buffer value at 1350^oC, 1atm) to 13 (beyond Iron-Wustite buffer) with duration going from 15 min to 24 hours. Effect of Fe content and pressure are not taken into account in the present study, as it would result in a multiplication of parameters, making results more difficult to interpret. Optical spectroscopy shows that Ni2+, is mainly 5- and 4-coordinated in the initial composition (^5[Ni]/^4[Ni]=7,14). Optical spectra shows an important evolution with reduction, indicating that modifications occurs in the glass structure around Ni2+. ^5[Ni]/^4[Ni] ratio decrease with oxygen fugacity. The apparition of metallic Ni in the glass is not the only origin of the varitation of the optical spectra. EXAF and XANES data, showing a strong evolution with the glass reduction, will be also discussed.

  8. Interaction between sulphide and H 2O in silicate melts

    NASA Astrophysics Data System (ADS)

    Stelling, Jan; Behrens, Harald; Wilke, Max; Göttlicher, Jörg; Chalmin-Aljanabi, Emilie

    2011-06-01

    Reaction between dissolved water and sulphide was experimentally investigated in soda-lime-silicate (NCS) and sodium trisilicate (NS3) melts at temperatures from 1000 to 1200 °C and pressures of 100 or 200 MPa in internally heated gas pressure vessels. Diffusion couple experiments were conducted at water-undersaturated conditions with one half of the couple being doped with sulphide (added as FeS or Na 2S; 1500-2000 ppm S by weight) and the other with H 2O (˜3.0 wt.%). Additionally, two experiments were performed using a dry NCS glass cylinder and a free H 2O fluid. Here, the melt was water-saturated at least at the melt/fluid interface. Profiling by electron microprobe (sulphur) and infrared microscopy (H 2O) demonstrate that H 2O diffusion in the melts is faster by 1.5-2.3 orders of magnitude than sulphur diffusion and, hence, H 2O can be considered as a rapidly diffusing oxidant while sulphur is quasi immobile in these experiments. In Raman spectra a band at 2576 cm -1 appears in the sulphide - H 2O transition zone which is attributed to fundamental S-H stretching vibrations. Formation of new IR absorption bands at 5025 cm -1 (on expense of the combination band of molecular H 2O at 5225 cm -1) and at 3400 cm -1 was observed at the front of the in-diffusing water in the sulphide bearing melt. The appearance and intensity of these two IR bands is correlated with systematic changes in S K-edge XANES spectra. A pre-edge excitation at 2466.5 eV grows with increasing H 2O concentration while the sulphide peak at 2474.0 eV decreases in intensity relative to the peak at 2477.0 eV and the feature at 2472.3 eV becomes more pronounced (all energies are relative to the sulphate excitation, calibrated to 2482.5 eV). The observations by Raman, IR and XANES spectroscopy indicate a well coordinated S 2- - H 2O complex which was probably formed in the glasses during cooling at the glass transition. No oxidation of sulphide was observed in any of the diffusion couple

  9. New surveys of the Chesapeake Bay impact structure suggest melt pockets and target-structure effect

    USGS Publications Warehouse

    Shah, A.K.; Brozena, J.; Vogt, P.; Daniels, D.; Plescia, J.

    2005-01-01

    We present high-resolution gravity and magnetic field survey results over the 85-km-diameter Chesapeake Bay impact structure. Whereas a continuous melt sheet is anticipated at a crater this size, shallow-source magnetic field anomalies of ???100 nT instead suggest that impact melt pooled in kilometer-scaled pockets surrounding the base of a central peak. A central anomaly of ???300 nT may represent additional melt or rock that underwent shock-induced remagnetization. Models predict that the total volume of the melt ranges from ???0.4 to 10 km3, a quantity that is several orders of magnitude smaller than expected for an impact structure this size. However, this volume is within predictions given a transient crater of diameter of 20-40 km for a target covered with water and sedimentary deposits such that melt fragments were widely dispersed at the time of impact. Gravity data delineate a gently sloping inner basin and a central peak via a contrast between crystalline and sedimentary rock. Both features are ovoid, oriented parallel to larger preimpact basement structures. Conceptual models suggest how lateral differences in rock strength due to these preimpact structures helped to shape the crater's morphology during transient-crater modification. ?? 2005 Geological Society of America.

  10. The dissolution of carbon doixide in silicate melts

    NASA Astrophysics Data System (ADS)

    Nowak, M.; Spickenbom, K.; Porbatzki, D.

    2003-04-01

    Carbon dioxide and H_2O are the two most abundant volatile components in Earth's crust, mantle, and in magmatic liquids. In contrast to H_2O there is still little information about the dissolution mechanism of CO_2 in silicate melts. First annealing experiments of CO_2-bearing albitic and dacitic glasses near the glass transition temperature at 0.5 GPa demonstrate that in contrast to previous suggestions [1] the equilibrium of the homogeneous CO_2 species reaction CO_2 (melt) + O2- (melt) = CO_32- (melt) shifts towards molecular CO_2 with increasing temperature [2]. This behaviour was recently confirmed for dissolved CO_2 in jadeitic glasses [3]. In order to provide more insights into the thermodynamics and kinetics of CO_2 in silicate melts we performed additional annealing experiments with dacitic and albitic glasses, especially with different run times. Glass cylinders containing 0.15--0.2 wt% CO_2 were synthesized at 1603 K and 0.5 GPa and rapidly quenched to room temperature. Glass slabs 2--3 mm in height were used for time dependent annealing experiments at ambient P, 0.5 GPa, and at 673--973 K. Run durations were 1--1000 min. MIR micro-spectroscopy was used to determine the peak areas of the molecular CO_2 band at 2350 cm-1 and the CO_32- band system at 1800 to 1250 cm-1. In the temperature range 673--973 K the CO_2 speciation shifts significantly towards molecular CO_2 with increasing temperature, which is in agreement with [2,3]. The CO_2 species concentrations and an ideal solution model were used to derive values for the enthalpy Δ H^0 and entropy Δ S^0 of the homogeneous CO_2 species reaction, assuming that the CO_2 speciation reflects those at annealing temperatures (albitic composition: Δ H^0 = -12 ± 2 kJ mol-1 and Δ S^0 = -23 ± 3 J mol-1 K-1; dacitic composition: Δ H^0 = -29 ± 2 kJ mol-1 and Δ S^0 = -32 ± 3 J mol-1 K-1). Within error the thermodynamic values for dacitic composition derived from annealing experiments at ambient P and at 0

  11. Reinterpretation of reduction potential measurements done by linear sweep voltammetry in silicate melts

    NASA Technical Reports Server (NTRS)

    Colson, R. O.; Haskin, L. A.; Keedy, C. R.

    1991-01-01

    The equilibrium concentrations of Ni between silicate melt and Pt were determined experimentally as a function of oxygen fugacity. The results demonstrate that metallic species derived in linear sweep voltammetry experiments in silicate melts are diffusing into Pt electrodes and not into the melt, as was concluded by previoius studies. This requires reinterpretation of previous linear sweep voltammetry results and recalculation and correction of reported reduction potentials. This paper reports these corrected reduction potentials. Also reported are the activity coefficients for Ni in synthetic basalt and diopsidic melts and for Co in diopsidic melt.

  12. Density of hydrous silicate melt at the conditions of Earth's deep upper mantle

    NASA Astrophysics Data System (ADS)

    Matsukage, Kyoko N.; Jing, Zhicheng; Karato, Shun-Ichiro

    2005-11-01

    The chemical evolution of the Earth and the terrestrial planets is largely controlled by the density of silicate melts. If melt density is higher than that of the surrounding solid, incompatible elements dissolved in the melt will be sequestered in the deep mantle. Previous studies on dry (water-free) melts showed that the density of silicate melts can be higher than that of surrounding solids under deep mantle conditions. However, melts formed under deep mantle conditions are also likely to contain some water, which will reduce the melt density. Here we present data constraining the density of hydrous silicate melt at the conditions of ~410km depth. We show that the water in the silicate melt is more compressible than the other components, and therefore the effect of water in reducing melt density is markedly diminished under high-pressure conditions. Our study indicates that there is a range of conditions under which a (hydrous) melt could be trapped at the 410-km boundary and hence incompatible elements could be sequestered in the deep mantle, although these conditions are sensitive to melt composition as well as the composition of the surrounding mantle.

  13. The effects of sulfide composition on the solubility of sulfur in coexisting silicate melts

    NASA Astrophysics Data System (ADS)

    Smythe, Duane; Wood, Bernard; Kiseeva, Ekaterina

    2016-04-01

    The extent to which sulfur dissolves in silicate melts saturated in an immiscible sulfide phase is a fundamental question in igneous petrology and plays a primary role in the generation of magmatic ore deposits, volcanic degassing and planetary differentiation. Terrestrial sulfide melts often contain over 20 weight percent Ni + Cu, however, most experimental studies investigating sulfur solubility in silicate melt have been primarily concerned with the effects of silicate melt composition, and pure FeS has been use as the immiscible sulfide melt (O'Neill and Mavrogenes, 2002; Li and Ripley, 2005). To investigation of the effects of sulfide composition, in addition to those of temperature, pressure and silicate melt composition, on sulfur solubility in silicate melts, we have carried out a series of experiments done at pressures between 1.5 and 3 GPa and temperatures from 1400 to 1800C over a range of compositions of both the silicate and sulfide melt. We find that the solubility of sulfur in silicate melts drops significantly with the substitution of Ni and Cu for Fe in the immiscible sulfide melt, decreasing by approximately 40% at mole fractions of NiS + Cu2S of 0.4. Combining our results with those from the previous studies investigating sulfur solubility in silicate melts we have also found that solubility increases with increasing temperature and decreases pressure. These results show that without considering the composition of the immiscible sulfide phase the sulfur content of silicate melts can be significantly overestimated. This may serve to explain the relatively low sulfur concentrations in MORB melts, which previous models predict to be undersaturated in a sulfide phase despite showing chemical and textural evidence for sulfide saturation. Li, C. & Ripley, E. M. (2005). Empirical equations to predict the sulfur content of mafic magmas at sulfide saturation and applications to magmatic sulfide deposits. Mineralium Deposita 40, 218-230. O'Neill, H. S. C

  14. The effect of sulphur in silicate melt on partitioning of Ni and other trace elements

    NASA Astrophysics Data System (ADS)

    Wood, Bernard; Kiseeva, Ekaterina; Wohlers, Anke

    2016-04-01

    It has been suggested that variations in the sulphur contents of silicate melts affect the partitioning of trace chalcophile elements, particularly Ni, between silicate melt and crystalline phases such as olivine [1]. The general idea is that Ni (and other elements) complex with sulphur dissolved in the melt, thereby stabilising Ni in the melt and reducing the olivine-melt partition coefficient DNi. More recent experiments lead to the assertion that any sulphur effect, if present is small and can be ignored [2]. Experiments aimed at addressing this problem have, however, struggled with the difficulty that the maximum S contents of olivine- precipitating melts do not exceed ~0.5% even at sulphide saturation. Any effect is therefore difficult to establish unequivocally. Here we have taken advantage of the fact that experiments under strongly reducing conditions, where FeO activity in the silicate melt is very low lead to much higher concentrations of S than those associated with olivine precipitation. We have therefore investigated partitioning between sulphide melts and haplobasaltic silicate melt at concentrations of FeO between 0.3 and 10 weight% in order to investigate the "sulphur-effect" on partitioning. At the lowest FeO contents we are able to drive the S content of the melt to 10 weight% enabling the effects to be unequivocally established. We find that partitioning of strongly lithophile elements Nb, Ta, U, REE partition more strongly out of silicate melt as its S content increases. The effect is, surprisingly, predominantly due to the effect of S on the activity coefficient of FeO in the melt. In contrast strongly chalcophile Ni, Cu, Ag partition more strongly into the melt as its S content increases. This is due to a dramatic lowering of the activity coefficients of these elements in the silicate as S increases. Elements which show little effect of S include Pb, Co and In. The results enable us to predict the effects of sulphur on olivine-melt and

  15. Silicate and carbonate melt inclusions associated with diamonds in deeply subducted carbonate rocks

    NASA Astrophysics Data System (ADS)

    Korsakov, Andrey V.; Hermann, Jörg

    2006-01-01

    Deeply subducted carbonate rocks from the Kokchetav massif (Northern Kazakhstan) recrystallised within the diamond stability field (P = 4.5-6.0 GPa; T ≈ 1000 °C) and preserve evidence for ultra high-pressure carbonate and silicate melts. The carbonate rocks consist of garnet and K-bearing clinopyroxene embedded in a dolomite or magnesian calcite matrix. Polycrystalline magnesian calcite and polyphase carbonate-silicate inclusions occurring in garnet and clinopyroxene show textural features of former melt inclusions. The trace element composition of such carbonate inclusions is enriched in Ba and light rare earth elements and depleted in heavy rare earth elements with respect to the matrix carbonates providing further evidence that the inclusions represent trapped carbonate melt. Polyphase inclusions in garnet and clinopyroxene within a magnesian calcite marble, consisting mainly of a tight intergrowth of biotite + K-feldspar and biotite + zoisite + titanite, are interpreted to represent two different types of K-rich silicate melts. Both melt types show high contents of large ion lithophile elements but contrasting contents of rare earth elements. The Ca-rich inclusions display high REE contents similar to the carbonate inclusions and show a general trace element characteristic compatible with a hydrous granitic origin. Low SiO2 content in the silicate melts indicates that they represent residual melts after extensive interaction with carbonates. These observations suggest that hydrous granitic melts derived from the adjacent metapelites reacted with dolomite at ultra high-pressure conditions to form garnet, clinopyroxene - a hydrous carbonate melt - and residual silicate melts. Silicate and carbonate melt inclusions contain diamond, providing evidence that such an interaction promotes diamond growth. The finding of carbonate melts in deeply subducted crust might have important consequences for recycling of trace elements and especially C from the slab to the

  16. Final Report - Experiments and Models for Chemical Diffusion in Silicate Melts

    SciTech Connect

    Richter, Frank

    1999-10-01

    The final report describes experimental measurements of chemical diffusion and self-diffusion in silicate melts. The data are then used to validate a theoretical model for calculating the diffusion matrix of non-ideal liquids.

  17. Complexation of Sr in aqueous fluids equilibrated with silicate melts: effect of melt and fluid composition

    NASA Astrophysics Data System (ADS)

    Borchert, Manuela; Wilke, Max; Schmidt, Christian; Kvashnina, Kristina

    2010-05-01

    At crustal conditions, the fluid-melt partitioning of Sr is mainly controlled by the salinity of the fluid and the composition of the melt (Borchert et al., 2010). The data show a sharp increase in the Sr partition coefficient with the alumina saturation index (ASI) to a maximum of 0.3 at an ASI of 1.05. Because fluid-melt partitioning of a given element depends on its complexation in the fluid and its incorporation in the melt, these data imply a change in the Sr speciation at least one of the two phases. For silicate melts, Kohn et al. (1990) found only small changes in the first coordination shell of Sr in a suite of melts with various degrees of polymerization, and argued that incorporation of Sr in the melt should not play a major role in controlling Sr partitioning. For the aqueous fluid, Bai and Koster van Groos (1999) and Webster et al. (1989) suggested a control of the Sr partition coefficient by SrCl2 complexes based on the correlation between partition coefficient and Cl concentration in the fluid after quenching. Both hypotheses cannot explain our partitioning data. Thus, new information on Sr complexation is required. Here, we studied the complexation of Sr in peraluminous or peralkaline melt dissolved in aqueous fluids in-situ at elevated PT conditions using hydrothermal diamond-anvil cells (HDAC) and X-ray absorption near edge structure (XANES) spectroscopy. The starting materials were peraluminous or peralkaline glass and H2O or a chloridic solution. The glass was doped with high concentrations of 5000 or 10000 ppm Sr. We used bulk compositions with 10 to 15 wt.% glass to ensure that the melt was completely dissolved in the fluid at high PT conditions. For qualitative evaluation, we analyzed the starting glasses and various crystalline compounds and standard solutions. The experiments were performed at beamline ID26 at ESRF (Grenoble, France) using a high resolution emission spectrometer and Si(311) monochromator crystals for high resolution and Si

  18. Water solubility in rhyolitic silicate melts at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Ryan, Amy; Russell, Kelly; Nichols, Alexander; Porritt, Lucy; Friedlander, Elizabeth

    2014-05-01

    temperatures, though slight, produces a marked change in maximum run product porosity from 50 to 70% through the temperature series, illuminating the effect of retrograde solubility at conduit- and surface-relevant pressures. The readiness of a rhyolitic silicate melt not only to produce more bubbles at higher temperatures, but also to resorb existing bubbles during cooling has important implications for magmatic fragmentation, flow of lava, and welding processes.

  19. Sulfur Saturation Limits in Silicate Melts and their Implications for Core Formation Scenarios for Terrestrial Planets

    NASA Technical Reports Server (NTRS)

    Holzheid, Astrid; Grove, Timothy L.

    2002-01-01

    This study explores the controls of temperature, pressure, and silicate melt composition on S solubility in silicate liquids. The solubility of S in FeO-containing silicate melts in equilibrium with metal sulfide increases significantly with increasing temperature but decreases with increasing pressure. The silicate melt structure also exercises a control on S solubility. Increasing the degree of polymerization of the silicate melt structure lowers the S solubility in the silicate liquid. The new set of experimental data is used to expand the model of Mavrogenes and O'Neill(1999) for S solubility in silicate liquids by incorporating the influence of the silicate melt structure. The expected S solubility in the ascending magma is calculated using the expanded model. Because the negative pressure dependence of S solubility is more influential than the positive temperature dependence, decompression and adiabatic ascent of a formerly S-saturated silicate magma will lead to S undersaturation. A primitive magma that is S-saturated in its source region will, therefore, become S-undersaturated as it ascends to shallower depth. In order to precipitate magmatic sulfides, the magma must first cool and undergo fractional crystallization to reach S saturation. The S content in a metallic liquid that is in equilibrium with a magma ocean that contains approx. 200 ppm S (i.e., Earth's bulk mantle S content) ranges from 5.5 to 12 wt% S. This range of S values encompasses the amount of S (9 to 12 wt%) that would be present in the outer core if S is the light element. Thus, the Earth's proto-mantle could be in equilibrium (in terms of the preserved S abundance) with a core-forming metallic phase.

  20. Occurrence of Siliceous Impact Melt in Netschaëvo IIE? A FIB-TEM Study

    NASA Astrophysics Data System (ADS)

    Hamann, C.; Van Roosbroek, N.; Greshake, A.; Pittarello, L.; Hecht, L.; Debaille, V.; Wirth, R.; Claeys, Ph.

    2015-07-01

    A silicate inclusion in a sample of the Netschaëvo IIE iron meteorite was studied with FIB-TEM. We present petrographic features indicating that this inclusion is quenched impact melt and suggest that Netschaëvo is an impact melt breccia.

  1. The effect of melt composition on the partitioning of oxidized sulfur between silicate melts and magmatic volatiles

    NASA Astrophysics Data System (ADS)

    Zajacz, Zoltán

    2015-06-01

    Experiments were conducted at 500 MPa and 1240 °C in a piston cylinder apparatus to assess the effect of melt composition on the melt/volatile partition coefficient of sulfur (DSmelt/volatile) , which was used as a measure of the silicate melt's capacity to dissolve oxidized sulfur species. Iron-free, three- and four-component silicate melts were equilibrated with H2O-S fluids with sulfur concentrations ⩽2 mol% at an oxygen fugacity imposed by the Re-ReO2 buffer (1.4 log units above the Ni-NiO buffer). At these conditions, SO2 (S4+) is predicted to be the dominant sulfur species in the volatile phase and sulfate (S6+) is the dominant sulfur species in the silicate melt. The values of DSmelt /volatile were calculated by mass balance. The results show that DSmelt /volatile values increase exponentially with decreasing the degree of polymerization of the silicate melt structure. For example, in calcium-aluminosilicate melts, DSmelt /volatile changes from 0.005 to 0.3 as the degree of melt polymerization changes from the equivalent of a rhyolite to the equivalent of a basalt. At a constant degree of melt polymerization, DSmelt /volatile in equilibrium with sodium-aluminosilicate (NAS) melts is more than an order of magnitude higher than in equilibrium with calcium-aluminosilicate (CAS) melts, and more than two orders of magnitude higher than in equilibrium with magnesium-aluminosilicate (MAS) melts. The value of DSmelt /volatile changes from 0.014 in MAS glasses to 3.4 in NAS glasses for the most depolymerized compositions in each series. Potassium has a similar effect on sulfate dissolution to that of Na. The variation of DSmelt /volatile in equilibrium with various calcium-sodium aluminosilicate (CNAS), magnesium-sodium aluminosilicate (MNAS) and magnesium-potassium aluminosilicate (MKAS) melts indicates that alkalis are only available for sulfate complexation when they are present in excess compared to the required amount to charge balance for the Si4+ to Al3

  2. Carbon-dioxide-rich silicate melt in the Earth's upper mantle.

    PubMed

    Dasgupta, Rajdeep; Mallik, Ananya; Tsuno, Kyusei; Withers, Anthony C; Hirth, Greg; Hirschmann, Marc M

    2013-01-10

    The onset of melting in the Earth's upper mantle influences the thermal evolution of the planet, fluxes of key volatiles to the exosphere, and geochemical and geophysical properties of the mantle. Although carbonatitic melt could be stable 250 km or less beneath mid-oceanic ridges, owing to the small fraction (∼0.03 wt%) its effects on the mantle properties are unclear. Geophysical measurements, however, suggest that melts of greater volume may be present at ∼200 km (refs 3-5) but large melt fractions are thought to be restricted to shallower depths. Here we present experiments on carbonated peridotites over 2-5 GPa that constrain the location and the slope of the onset of silicate melting in the mantle. We find that the pressure-temperature slope of carbonated silicate melting is steeper than the solidus of volatile-free peridotite and that silicate melting of dry peridotite + CO(2) beneath ridges commences at ∼180 km. Accounting for the effect of 50-200 p.p.m. H(2)O on freezing point depression, the onset of silicate melting for a sub-ridge mantle with ∼100 p.p.m. CO(2) becomes as deep as ∼220-300 km. We suggest that, on a global scale, carbonated silicate melt generation at a redox front ∼250-200 km deep, with destabilization of metal and majorite in the upwelling mantle, explains the oceanic low-velocity zone and the electrical conductivity structure of the mantle. In locally oxidized domains, deeper carbonated silicate melt may contribute to the seismic X-discontinuity. Furthermore, our results, along with the electrical conductivity of molten carbonated peridotite and that of the oceanic upper mantle, suggest that mantle at depth is CO(2)-rich but H(2)O-poor. Finally, carbonated silicate melts restrict the stability of carbonatite in the Earth's deep upper mantle, and the inventory of carbon, H(2)O and other highly incompatible elements at ridges becomes controlled by the flux of the former. PMID:23302861

  3. Termochemical Models For Slags and Silicate Melts, Review and Perspectives

    NASA Astrophysics Data System (ADS)

    Ottonello, G.

    Thermochemical models devoted to the comprehension of reactive and mixing properties of silicate melts and slags may be roughly grouped into four main classes: 1) fictive chemical; 2) quasi chemical; 3) fictive structural; 4) polymeric. In the first class we may group the fictive regular mixture approach of Ghiorso and Carmichael [1,2]and its extensions [3-5]and the subregular model of Berman and Brown [6]. To the second class belong the modified quasi chemical approach of Pelton and coworkers [7,8] , and the Kapoor - Froberg cellular model and its extensions [9-11]. The third class has much to share with the second one (and indeed the cellular model could be ascribed to this class as well). To this class belong the "central surround model" of Sastri and Lahiri [12] , the associated solution models of Bjorkman [13], Hastie and coworkers [14]and Goel and coworkers [15], the two sublattice model of Hillert and coworkers [16]and the polynomial expansions of Hoch and Arpshofen [17] . The fourth class encompasses the models of Masson[18-20] , Toop-Samis [21,22]and its extensions [23-25] . The phylosophy beyond each one of the four classes is basically different. Benefits and drawbacks are present in any of them, and applications are often limited to simple systems (or to sufficiently complex systems, in the case of arbitrary deconvolutions of type 1) and to limited P-T ranges. The crucial aspects of the various models will be outlined to some extent. It will be shown that, often, model conflictuality is only appartent and that, in some cases, model failure is unperceived by acritical utilizers. New perspectives in the future research devoted to the comprehension of melt reactivity in compositionally complex systems, with special enphasis on the solubility of gaseous components and unmixing, will be finally discussed. References: [1] Ghiorso M.S. and Carmichael I.S.E. (1980) Contrib. Mineral. Petrol., 71, 323-342. [2] Ghiorso M.S., Carmichael I.S.E., Rivers M.L. and Sack

  4. Energetics of silicate melts from thermal diffusion studies

    SciTech Connect

    Walker, D.

    1992-07-01

    Efforts are reported in the following areas: laboratory equipment (multianvils for high P/T work, pressure media, SERC/DL sychrotron), liquid-state thermal diffusion (silicate liquids, O isotopic fractionation, volatiles, tektites, polymetallic sulfide liquids, carbonate liquids, aqueous sulfate solutions), and liquid-state isothermal diffusion (self-diffusion, basalt-rhyolite interdiffusion, selective contamination, chemical diffusion).

  5. Chalcophile element partitioning into magmatic sulphides: the effect of silicate melt composition

    NASA Astrophysics Data System (ADS)

    Kiseeva, Kate; Wood, Bernard

    2016-04-01

    Partitioning of many elements between sulphide and silicate melts is a function of the FeO content of the silicate liquid (Kiseeva and Wood, 2013). The theoretical relationship is a linear one between LogDM (DM=[M]sulph/[M]sil) and -log[FeO] with a slope of n/2, where n is the valency of trace element M. In practice we find that the slope deviates from the theoretical one because of the presence of oxygen in the sulphide. In our recent study we investigated the effects of sulphide composition and temperature on chalcophile element partitioning between sulphide and silicate liquids (Kiseeva and Wood, 2015). We have concluded that partitioning of most chalcophile elements is a strong function of the oxygen (or FeO) content of the sulphide. As expected, lithophile elements partition more strongly into sulphide as its oxygen content increases, while chalcophile elements enter sulphide less readily with increasing oxygen. The effect of Ni and Cu content of sulphide is significantly smaller than the effect of oxygen, while the effects of temperature are large only for a number of elements (such as Ni, Cu, Ag). In this study we show that in addition to the effect of sulphide composition, for certain elements the effect of silicate melt composition on sulphide/silicate partitioning can be quite large. For instance, within the range of NBO/T between 0.5 and 2 the DTlsulph/sil changes in order of magnitude. For the elements, like Pb, partition coefficient does not seem to change much with the silicate melt composition, while for Sb the effect of the silicate melt composition on D is a factor of 3. Partitioning of chalcophile elements into more evolved, alkali-rich and felsic magmas is estimated to be very different from the partitioning into basaltic melts, mainly due to the strong effects of temperature and alkali components. Although it is highly likely that sulphide is in solid form at liquidus temperatures for dacite and rhyolite and thus the partitioning of chalcophile

  6. CHEMISTRY OF IMPACT-GENERATED SILICATE MELT-VAPOR DEBRIS DISKS

    SciTech Connect

    Visscher, Channon; Fegley, Bruce Jr.

    2013-04-10

    In the giant impact theory for lunar origin, the Moon forms from material ejected by the impact into an Earth-orbiting disk. Here we report the initial results from a silicate melt-vapor equilibrium chemistry model for such impact-generated planetary debris disks. In order to simulate the chemical behavior of a two-phase (melt+vapor) disk, we calculate the temperature-dependent pressure and chemical composition of vapor in equilibrium with molten silicate from 2000 to 4000 K. We consider the elements O, Na, K, Fe, Si, Mg, Ca, Al, Ti, and Zn for a range of bulk silicate compositions (Earth, Moon, Mars, eucrite parent body, angrites, and ureilites). In general, the disk atmosphere is dominated by Na, Zn, and O{sub 2} at lower temperatures (<3000 K) and SiO, O{sub 2}, and O at higher temperatures. The high-temperature chemistry is consistent for any silicate melt composition, and we thus expect abundant SiO, O{sub 2}, and O to be a common feature of hot, impact-generated debris disks. In addition, the saturated silicate vapor is highly oxidizing, with oxygen fugacity (f{sub O{sub 2}}) values (and hence H{sub 2}O/H{sub 2} and CO{sub 2}/CO ratios) several orders of magnitude higher than those in a solar-composition gas. High f{sub O{sub 2}} values in the disk atmosphere are found for any silicate composition because oxygen is the most abundant element in rock. We thus expect high oxygen fugacity to be a ubiquitous feature of any silicate melt-vapor disk produced via collisions between rocky planets.

  7. Chemistry of Impact-generated Silicate Melt-vapor Debris Disks

    NASA Astrophysics Data System (ADS)

    Visscher, Channon; Fegley, Bruce, Jr.

    2013-04-01

    In the giant impact theory for lunar origin, the Moon forms from material ejected by the impact into an Earth-orbiting disk. Here we report the initial results from a silicate melt-vapor equilibrium chemistry model for such impact-generated planetary debris disks. In order to simulate the chemical behavior of a two-phase (melt+vapor) disk, we calculate the temperature-dependent pressure and chemical composition of vapor in equilibrium with molten silicate from 2000 to 4000 K. We consider the elements O, Na, K, Fe, Si, Mg, Ca, Al, Ti, and Zn for a range of bulk silicate compositions (Earth, Moon, Mars, eucrite parent body, angrites, and ureilites). In general, the disk atmosphere is dominated by Na, Zn, and O2 at lower temperatures (<3000 K) and SiO, O2, and O at higher temperatures. The high-temperature chemistry is consistent for any silicate melt composition, and we thus expect abundant SiO, O2, and O to be a common feature of hot, impact-generated debris disks. In addition, the saturated silicate vapor is highly oxidizing, with oxygen fugacity (f_O_2) values (and hence H2O/H2 and CO2/CO ratios) several orders of magnitude higher than those in a solar-composition gas. High f_O_2 values in the disk atmosphere are found for any silicate composition because oxygen is the most abundant element in rock. We thus expect high oxygen fugacity to be a ubiquitous feature of any silicate melt-vapor disk produced via collisions between rocky planets.

  8. Pt, Au, Pd and Ru Partitioning Between Mineral and Silicate Melts: The Role of Metal Nanonuggets

    NASA Technical Reports Server (NTRS)

    Malavergne, V.; Charon, E.; Jones, J.; Agranier, A.; Campbell, A.

    2012-01-01

    The partition coefficients of Pt and other Pt Group Elements (PGE) between metal and silicate D(sub Metal-Silicate) and also between silicate minerals and silicate melts D(sub Metal-Silicate) are among the most challenging coefficients to obtain precisely. The PGE are highly siderophile elements (HSE) with D(sub Metal-Silicate) >10(exp 3) due to the fact that their concentrations in silicates are very low (ppb to ppt range). Therefore, the analytical difficulty is increased by the possible presence of HSE-rich-nuggets in reduced silicate melts during experiments). These tiny HSE nuggets complicate the interpretation of measured HSE concentrations. If the HSE micro-nuggets are just sample artifacts, then their contributions should be removed before calculations of the final concentration. On the other hand, if they are produced during the quench, then they should be included in the analysis. We still don't understand the mechanism of nugget formation well. Are they formed during the quench by precipitation from precursor species dissolved homogeneously in the melts, or are they precipitated in situ at high temperature due to oversaturation? As these elements are important tracers of early planetary processes such as core formation, it is important to take up this analytical and experimental challenge. In the case of the Earth for example, chondritic relative abundances of the HSE in some mantle xenoliths have led to the concept of the "late veneer" as a source of volatiles (such as water) and siderophiles in the silicate Earth. Silicate crystal/liquid fractionation is responsible for most, if not all, the HSE variation in the martian meteorite suites (SNC) and Pt is the element least affected by these fractionations. Therefore, in terms of reconstructing mantle HSE abundances for Mars, Pt becomes a very important player. In the present study, we have performed high temperature experiments under various redox conditions in order to determine the abundances of Pt, Au

  9. Atomistic insight into viscosity and density of silicate melts under pressure.

    PubMed

    Wang, Yanbin; Sakamaki, Tatsuya; Skinner, Lawrie B; Jing, Zhicheng; Yu, Tony; Kono, Yoshio; Park, Changyong; Shen, Guoyin; Rivers, Mark L; Sutton, Stephen R

    2014-01-01

    A defining characteristic of silicate melts is the degree of polymerization (tetrahedral connectivity), which dictates viscosity and affects compressibility. While viscosity of depolymerized silicate melts increases with pressure consistent with the free-volume theory, isothermal viscosity of polymerized melts decreases with pressure up to ~3-5 GPa, above which it turns over to normal (positive) pressure dependence. Here we show that the viscosity turnover in polymerized liquids corresponds to the tetrahedral packing limit, below which the structure is compressed through tightening of the inter-tetrahedral bond angle, resulting in high compressibility, continual breakup of tetrahedral connectivity and viscosity decrease with increasing pressure. Above the turnover pressure, silicon and aluminium coordination increases to allow further packing, with increasing viscosity and density. These structural responses prescribe the distribution of melt viscosity and density with depth and play an important role in magma transport in terrestrial planetary interiors. PMID:24476847

  10. Atomistic insight into viscosity and density of silicate melts under pressure

    NASA Astrophysics Data System (ADS)

    Wang, Yanbin; Sakamaki, Tatsuya; Skinner, Lawrie B.; Jing, Zhicheng; Yu, Tony; Kono, Yoshio; Park, Changyong; Shen, Guoyin; Rivers, Mark L.; Sutton, Stephen R.

    2014-01-01

    A defining characteristic of silicate melts is the degree of polymerization (tetrahedral connectivity), which dictates viscosity and affects compressibility. While viscosity of depolymerized silicate melts increases with pressure consistent with the free-volume theory, isothermal viscosity of polymerized melts decreases with pressure up to ~3-5 GPa, above which it turns over to normal (positive) pressure dependence. Here we show that the viscosity turnover in polymerized liquids corresponds to the tetrahedral packing limit, below which the structure is compressed through tightening of the inter-tetrahedral bond angle, resulting in high compressibility, continual breakup of tetrahedral connectivity and viscosity decrease with increasing pressure. Above the turnover pressure, silicon and aluminium coordination increases to allow further packing, with increasing viscosity and density. These structural responses prescribe the distribution of melt viscosity and density with depth and play an important role in magma transport in terrestrial planetary interiors.

  11. Redox Viscosity of Iron Rich Silicate Melts - Martian Mantle Analogues.

    NASA Astrophysics Data System (ADS)

    Dingwell, D. B.

    2004-12-01

    The dependence of shear viscosity on the oxidation state of ferrosilicate melts has been measured using the concentric cylinder method and a gas mixing furnace. Two different simple Fe-bearing systems have been studied to date: (i) anorthite-diopside eutectic composition (AnDi) with variable amount of Fe (up to 20 wt%) as a basalt analogue and (ii) sodium disilicate (NS2 up to 30 wt % Fe). In addition, the compositional range has been extended to include the more complex SNC meteorite composition, a composition more relevant to Mars. The measurements were performed under air, CO2 and CO2-CO mixture at 1 atm and in a temperature range of 1300 to 1350 \\ºC. The experimental procedure involve a continuous measurement of viscosity during stepwise reduction state. The melt was reduced by flowing CO2 and then successively reducing mixtures of CO2-CO through the alumina muffle tube. Gas flow rates were electronically controlled using Tylan mass flow controllers and oxygen fugacity was directly measured using a sensor and calculated with Nernst equation. The composition and oxidation state of the melt was monitored by obtaining a melt sample after each redox equilibrium step. The melts were sampled by dipping an alumina rod into the sample and drawing out a drop of liquid, which was then plunged into water for quenching. The resulting glasses were analyzed by electron microprobe, and the volumetric potassium dichromate titration were employed to determine FeO. In addition, the redox dependence of viscosity of our samples have been compared with data from literature (Mysen et al. 1985, Dingwell and Virgo, 1988; Dingwell 1989, Dingwell 1991). The viscosity of all melts investigated herein decreases with melt reduction. The viscosity decrease is, in general, a nonlinear function of oxidation state expressed as Fe2+/Fetot and can be fitted using logarithmic equation.

  12. Activity composition relationships in silicate melts. Final report

    SciTech Connect

    Glazner, A.F.

    1990-12-31

    Equipment progress include furnace construction and electron microprobe installation. The following studies are underway: phase equilibria along basalt-rhyolite mixing line (olivine crystallization from natural silicic andensites, distribution of Fe and Mg between olivine and liquid, dist. of Ca and Na between plagioclase and liquid), enthalpy-composition relations in magmas (bulk heat capacity of alkali basalt), density model for magma ascent and contamination, thermobarometry in igneous systems (olivine/plagioclase phenocryst growth in Quat. basalt), high-pressure phase equilibria of alkali basalt, basalt-quartz mixing experiments, phase equilibria of East African basalts, and granitic minerals in mafic magma. (DLC)

  13. Ionic-polymeric models and the amphoteric behavior of water in silicate melts

    NASA Astrophysics Data System (ADS)

    Moretti, R.

    2012-04-01

    In silicate melts it is almost impossible to readily distinguish solute and solvent like in aqueous solutions. The anionic framework of silicate melts, in fact, makes solute and solvents so intimately related that one cannot identify a solvation shell and identify directly, from structural studies, the complexes needed to define acid-base reactions. Therefore, the distinction between solute and solvent becomes blurred in systems such as silicate melts, because speciation is not only complex but changes with the marked depolymerization of the silicate framework that obtains from pure SiO2 to metal-oxide rich compositions. These features do not allow proper understanding of the actual physico-chemical role of many species detected by conventional techniques, a fact which can lead to confusing notation. However, these may not be serious limits to account correctly for the acid-base reactions that take place in every kind of magmatic setting, provided a 'syntax' describing the effective interactions among significative cationic and anionic entities. In particular, the syntax for acid-base exchanges is needed such that constituting oxides (i.e. chemical components) can be treated independently of (but not necessarily extraneous to) structural features in defining such entities. So-called ionic-polymeric models highlight the mutual correspondence between polymerization and acid-base properties of dissolved oxides through the Lux-Flood formalism for molten oxides. They thus provide the syntax to write chemical exchanges, but have no pretension to structural description. In fact the concept of melt polymerization is used to identify basic anions and cations that can be used, along with their formal charge, to describe effectively acid-base interactions taking place in melts. In this respect, an example is given by the description of the amphoteric behavior of water dissolved on melts, hence water autoprotolysis. Although it exerts a profound influence on properties of

  14. Experimental Compressibility of CO2 in Silicate Melts and the Effect on Planetary Differentiation

    NASA Astrophysics Data System (ADS)

    Agee, C. B.; Duncan, M. S.; Dreeland, L. E.

    2008-12-01

    High pressure experiments using the sink/float method have bracketed the density of carbonated partial melt of peridotite and carbonated Apollo 14 black glass melt at high pressures and temperatures. The experiments were designed to determine the compressibility of CO2 in silicate melts and allow prediction of crystal-liquid density crossovers in CO2-bearing planetary magmas. The silicate melt compositions were synthetic mixtures of reagent oxides with CO2 added in the form of CaCO3. Samples were contained in compression-sealed molybdenum capsules. Sink/float marker spheres implemented were gem quality synthetic forsterite (Fo100) and San Carlos olivine (Fo91). Experimental run times were 30 seconds, thus minimizing sphere-liquid reactions and liquid reaction with capsule and pressure media. CO2 (total) in the quench melt run products was estimated by electron microprobe analyses of carbon and oxygen. All experiments were carried out in a Walker multi-anvil apparatus or a Quick Press piston-cylinder device at the Institute of Meteoritics, University of New Mexico. The densities of peridotite partial melt with 5 wt % CO2 and the same peridotite partial melt with no CO2 were determined at 4.3 GPa and ~1825 C. Using the density difference between the carbonated and non-carbonated melts we calculate a partial molar volume of CO2 in peridotite partial melt of approximately 18 cm3mol-1 at these conditions. This represents a 35% decrease in VCO2 compared to estimates for VCO2 at 1-bar (Liu and Lange, 2003), indicating a high compressibility for CO2 in silicate melt over the range 0-4 GPa. Our value of VCO2 is similar to that of estimated for basalt at 19.5 GPa (Ghosh et al., 2007), suggesting that the compressibility of CO2 in silicate melt decreases significantly with pressure, although more experiments are needed to confirm this possibility. Our experiments on Apollo 14 black glass are the first of their kind to simultaneously determine melt density and CO2 solubility

  15. Partitioning of copper between olivine, orthopyroxene, clinopyroxene, spinel, garnet and silicate melts at upper mantle conditions

    NASA Astrophysics Data System (ADS)

    Liu, Xingcheng; Xiong, Xiaolin; Audétat, Andreas; Li, Yuan; Song, Maoshuang; Li, Li; Sun, Weidong; Ding, Xing

    2014-01-01

    Previously published Cu partition coefficients (DCu) between silicate minerals and melts cover a wide range and have resulted in large uncertainties in model calculations of Cu behavior during mantle melting. In order to obtain true DCumineral/melt values, this study used Pt95Cu05 alloy capsules as the source of Cu to experimentally determine the DCu between olivine (ol), orthopyroxene (opx), clinopyroxene (cpx), spinel (spl), garnet (grt) and hydrous silicate melts at upper mantle conditions. Three synthetic silicate compositions, a Komatiite, a MORB and a Di70An30, were used to produce these minerals and melts. The experiments were conducted in piston cylinder presses at 1.0-3.5 GPa, 1150-1300 °C and oxygen fugacities (fO2) of from ∼2 log units below to ∼5 log units above fayalite-magnetite-quartz (FMQ). The compositions of minerals and quenched melts in the run products were measured with EMP and LA-ICP-MS. Attainment of equilibrium is verified by reproducible DCu values obtained at similar experimental conditions but different durations. The results show that DCu for ol/, opx/, spl/ and possibly cpx/melt increase with increasing fO2 when fO2 > FMQ + 1.2, while DCu for cpx/ and spl/melt also increase with increasing Na2O in cpx and Fe2O3 in spinel, respectively. In the investigated P-T-fO2 conditions, the DCumineral/melt values are 0.04-0.14 for ol, 0.04-0.09 for opx, 0.02-0.23 for cpx, 0.19-0.77 for spl and 0.03-0.05 for grt. These results confirm that Cu is highly incompatible (DCu < ∼0.2) in all the silicate minerals and oxides of the upper mantle with the exception of the high-Fe spinel, in which Cu is moderately incompatible (DCu = 0.4-0.8) and thus Cu will be enriched in the derived melts during mantle partial melting and magmatic differentiation if sulfide is absent. These experimental DCu values are used to assess the controls on Cu behavior during mantle melting. The model results suggest that MORBs and most arc basalts must form by sulfide

  16. Veins in Silicates of IIE Iron Mont Dieu II: Melt Migration Caused by Impact?

    NASA Astrophysics Data System (ADS)

    Van Roosbroek, N.; Debaille, V.; Pittarello, L.; Hecht, L.; Claeys, Ph.

    2014-09-01

    Mont Dieu II is a ~450kg meteorite classified as IIE iron. The primitive silicate inclusions can be linked to the H-chondrites. Thick metal veins with angular clasts crosscut these inclusions and could point to an impact-melt migration formation.

  17. The evolution of immiscible silicate and fluoride melts: Implications for REE ore-genesis

    NASA Astrophysics Data System (ADS)

    Vasyukova, O.; Williams-Jones, A. E.

    2016-01-01

    The Mid-Proterozoic peralkaline Strange Lake pluton (Québec-Labrador, Canada) exhibits extreme enrichment in high field strength elements (HFSE), including the rare earth elements (REE), particularly in pegmatites. On the basis of a study of melt inclusions, we proposed recently that fluoride-silicate melt immiscibility played an important and perhaps dominant role in concentrating the REE within the pluton. Here we present further evidence for silicate-fluoride immiscibility at Strange Lake from a sample of the hypersolvus granite, which contains an inclusion composed largely of REE and HFSE minerals. The inclusion (∼5 cm in diameter) comprises a narrow rim containing chevkinite-(Ce) and zircon in a fluorite matrix, a core of fluorbritholite-(Ce) and bastnäsite-(Ce) and a transition zone between the rim and the core consisting of a fine-grained intergrowth of bastnäsite-(Ce), gagarinite-(Y) and fluorite. We propose that the inclusion formed as a result of silicate-fluoride immiscibility, which occurred early in the emplacement history of the Strange Lake pluton, and that it represents the fluoride melt. After separation of the two melts, the boundary between them acted as a locus of crystallisation, where crystals formed repeatedly due to heterogeneous (surface catalysed) nucleation. Zircon crystallised shortly after melt phase separation, and was followed by the growth of perthite together with arfvedsonite and quartz. As a result, the silicate melt surrounding the fluoride inclusion became enriched in volatiles that facilitated crystallisation of progressively larger crystals in the inclusion; large crystals of arfvedsonite and perthite were succeeded by even larger crystals of quartz. Massive crystallisation of chevkinite-(Ce) followed, forming the rim of the inclusion. The fluoride melt, which constituted the matrix to the silicate minerals and chevkinite-(Ce), crystallised after chevkinite-(Ce), forming fluorbritholite-(Ce) and fluorite. Aqueous fluid

  18. Experimental calibration of a new oxybarometer for silicic magmas based on the partitioning of vanadium between magnetite and silicate melt

    NASA Astrophysics Data System (ADS)

    Arató, Róbert; Audétat, Andreas

    2016-04-01

    Oxygen fugacity is an important parameter in magmatic systems that affects the stability of mineral phases and fluid species. However, there is no well-established method to reconstruct the oxygen fugacity of slowly cooled magmas such as granite, for example, because existing oxybarometers (e.g., magnetite-ilmenite method) are susceptible to re-equilibration processes during slow cooling and thus lead to erroneous results when applied for granitic rocks. In this study, we aim at developing an oxybarometer that is based on the partitioning of vanadium (a redox-sensitive element) between magnetite inclusions and silicate melt inclusions preserved in quartz phenocrysts, where they were protected from subsolidus alteration and can be measured as entities by LA-ICP-MS. In the first - experimental - part of this study we investigated the effects of temperature (800-950 ° C), pressure (1-2 kbar), oxygen fugacity (from ΔFMQ+0.7 to ΔFMQ+4.0), magnetite composition, and melt composition on the partition coefficient of vanadium between magnetite and melt (DVmgt-melt). The experiments were carried out in cold-seal pressure vessels and the starting material was a mixture of V-doped haplogranite glasses or natural obsidian powder with variable aluminum saturation index (ASI), and synthetic, V-free magnetite of 10-20 μm grain size. The vanadium partition coefficient was found to depend strongly on oxygen fugacity, and to lesser (but still considerable) degrees on melt composition and temperature. A more than 1.5 log unit decrease in DVmgt-melt values with increasing oxygen fugacity can be explained by a change of the dominant valence state of V in the silicate melt. For a given oxygen fugacity buffer DVmgt-melt decreases with increasing temperature, but this reflects mostly the change in absolute fO2 values while the net temperature effect is in fact positive. DVmgt-melt depends significantly on melt composition, resulting in higher D-values with increasing aluminum

  19. Silicate melts density, buoyancy relations and the dynamics of magmatic processes in the upper mantle

    NASA Astrophysics Data System (ADS)

    Sanchez-Valle, Carmen; Malfait, Wim J.

    2016-04-01

    Although silicate melts comprise only a minor volume fraction of the present day Earth, they play a critical role on the Earth's geochemical and geodynamical evolution. Their physical properties, namely the density, are a key control on many magmatic processes, including magma chamber dynamics and volcanic eruptions, melt extraction from residual rocks during partial melting, as well as crystal settling and melt migration. However, the quantitative modeling of these processes has been long limited by the scarcity of data on the density and compressibility of volatile-bearing silicate melts at relevant pressure and temperature conditions. In the last decade, new experimental designs namely combining large volume presses and synchrotron-based techniques have opened the possibility for determining in situ the density of a wide range of dry and volatile-bearing (H2O and CO2) silicate melt compositions at high pressure-high temperature conditions. In this contribution we will illustrate some of these progresses with focus on recent results on the density of dry and hydrous felsic and intermediate melt compositions (rhyolite, phonolite and andesite melts) at crustal and upper mantle conditions (up to 4 GPa and 2000 K). The new data on felsic-intermediate melts has been combined with in situ data on (ultra)mafic systems and ambient pressure dilatometry and sound velocity data to calibrate a continuous, predictive density model for hydrous and CO2-bearing silicate melts with applications to magmatic processes down to the conditions of the mantle transition zone (up to 2773 K and 22 GPa). The calibration dataset consist of more than 370 density measurements on high-pressure and/or water-and CO2-bearing melts and it is formulated in terms of the partial molar properties of the oxide components. The model predicts the density of volatile-bearing liquids to within 42 kg/m3 in the calibration interval and the model extrapolations up to 3000 K and 100 GPa are in good agreement

  20. Growth of Diamond from a Carbonaceous Hydrous Silicate Melt: An Experimental Study

    NASA Astrophysics Data System (ADS)

    Fagan, A. J.; Luth, R. W.

    2007-12-01

    Diamond was grown in a hydrous halide-bearing silicate system at pressures and temperatures near those at which natural peridotitic diamonds form (1000-1300° C, 5-7 GPa) in the Earth' s upper mantle. The mechanisms by which diamonds are made within the earth is still unresolved, and many authors have suggested possible media from which diamonds precipitate; examples include mantle carbonates, sulphides and silicates (1-3). To date, little work has been conducted on silicate melts and the effect of mantle catalysts on diamond formation. This study used a hydrous silicate melt (HSM) to attempt to precipitate diamond. The primary experimental system was MgO-SiO2-C-H2O, with subsystems to document the addition of alkali halides (KCl and NaCl). Previous studies have concluded that alkali halides have a catalytic effect on diamond formation reactions and observed halides in inclusions in natural diamonds. Diamond was successfully grown on seed crystals at temperatures of 1400-1500° C and pressures of 6-7 GPa, in 3-4 hours. No spontaneous nucleation of diamond was observed during these experiments. No diamond growth was observed in experiments at < 1400° C and 6 GPa to date. The addition of KCl to the HSM system allowed diamond to form 200° C lower than the previously published minimum temperature of over 1600° C (3). The effect of NaCl and other catalysts are still under investigation. The starting compositions contain ~ 20.6wt% structural H2O. At run conditions, a hydrous melt coexisted with olivine and orthropyroxene, with the halides either dissolved in the melt or forming a separate brine. This study demonstrates that hydrous silicate melts, especially containing alkali halides, are a viable medium for diamond growth in the Earth' s upper mantle. 1) Arima et al, 2002; 2) Gunn & Luth, 2006; 3) Pal' yanov et al, 2007

  1. Water speciation in sodium silicate glasses (quenched melts): A comprehensive NMR study

    NASA Astrophysics Data System (ADS)

    Xue, X.; Kanzaki, M.; Eguchi, J.

    2012-12-01

    Dissolution mechanism of water is an important factor governing how the dissolved water affects the physical and thermodynamic properties of silicate melts and glasses. Our previous studies have demonstrated that 1H MAS NMR in combination with 29Si-1H and 27Al-1H double-resonance NMR experiments is an effective approach for unambiguously differentiating and quantifying different water species in quenched silicate melts (glasses). Several contrasting dissolution mechanisms have been revealed depending on the melt composition: for relatively polymerized melts, the formation of SiOH/AlOH species (plus molecular H2O) and depolymerization of the network structure dominate; whereas for depolymerized Ca-Mg silicate melts, free OH (e.g. MgOH) become increasingly important (cf. [1]). The proportion of free OH species has been shown to decrease with both increasing melt polymerization (silica content) and decreasing field strength of the network modifying cations (from Mg to Ca). Our previous 1H and 29Si MAS NMR results for hydrous Na silicate glasses of limited compositions (Na2Si4O9 and Na2Si2O5) were consistent with negligible free OH (NaOH) species and depolymerizing effect of water dissolution [2]. On the other hand, there were also other studies that proposed the presence of significant NaOH species in hydrous glasses near the Na2Si2O5 composition. The purpose of this study is apply the approach of combined 1H MAS NMR and double-resonance (29Si-1H and 23Na-1H) NMR to gain unambiguous evidence for the OH speciation in Na silicate glasses (melts) as a function of composition. Hydrous Na silicate glasses containing mostly ≤ 1 wt% H2O for a range of Na/Si ratios from 0.33 to 1.33 have been synthesized by rapidly quenching melts either at 0.2 GPa using an internally heated gas pressure vessel or at 1 GPa using a piston cylinder high-pressure apparatus. NMR spectra have been acquired using a 9.4 T Varian Unity-Inova spectrometer. The 29Si and 1H chemical shifts are

  2. Understanding Vesuvius magmatic processes: Evidence from primitive silicate-melt inclusions in medieval scoria clinopyroxenes (Terzigno formation)

    USGS Publications Warehouse

    Lima, A.; Belkin, H.E.; Torok, K.

    1999-01-01

    Microthermometric investigations of silicate-melt inclusions and electron microprobe analyses were conducted on experimentally homogenized silicate-melt inclusions and on the host clinopyroxenes from 4 scoria samples of different layers from the Mt. Somma-Vesuvius medieval eruption (Formazione di Terzigno, 893 A.D.). The temperature of homogenization, considered the minimum trapping temperature, ranges from 1190 to 1260??5 ??C for all clinopyroxene-hosted silicate melt inclusions. The major and minor-element compositional trends shown by Terzigno scoria and matrix glass chemical analysis are largely compatible with fractional crystallization of clinopyroxene and Fe-Ti oxides. Sulfur contents of the homogenized silicate-melt inclusions in clinopyroxene phenocrysts compared with that in the host scoria show that S has been significantly degassed in the erupted products; whereas, Cl has about the same abundance in the inclusions and in host scoria. Fluorine is low (infrequently up to 800 ppm) in the silicate-melt inclusions compared to 2400 ppm in the bulk scoria. Electron microprobe analyses of silicate-melt inclusions show that they have primitive magma compositions (Mg# = 75-91). The composition of the host clinopyroxene phenocrysts varies from typical plinian-related (Mg#???85) to non-plinian related (Mg#???85). The mixed source of the host clinopyroxenes and primitive nature of the silicate-melt inclusions implies that these phenocrysts, in part, may be residual and/or have a polygenetic origin. The similar variation trends of major and minor-elements between homogenized silicate-melt inclusions from the Terzigno scoria, and silicate-melt inclusions in olivine and diopside phenocrysts from plinian eruptions (Marianelli et al., 1995) suggest that the trapped inclusions represent melts similar to those that supplied the plinian and sub-plinian magma chambers. These geochemical characteristics suggest that the Vesuvius magmatic system retained a vestige of the most

  3. Rutile solubility and titanium coordination in silicate melts

    NASA Astrophysics Data System (ADS)

    Dickinson, James E., Jr.; Hess, Paul C.

    1985-11-01

    The solubility of rutile has been determined in a series of compositions in the K 2O-Al 2O 3-SiO 2 system ( K ∗ = K 2O /(K 2O + Al 2O 3) = 0.38-0.90), and the CaO-Al 2O 3-SiO 2 system ( C ∗ = CaO/(CaO + Al 2O 3) = 0.47-0.59 ). Isothermal results in the KAS system at 1325°C, 1400°C, and 1475°C show rutile solubility to be a strong function of the K ∗ ratio. For example, at 1475°C the amount of TiO 2 required for rutile saturation varies from 9.5 wt% ( K ∗ = 0.38 ) to 11.5 wt% ( K ∗ = 0.48 ) to 41.2 wt% ( K ∗ = 0.90 ). In the CAS system at 1475°C, rutile solubility is not a strong function of C ∗. The amount of TiO 2 required for saturation varies from 14 wt% ( C ∗ = 0.48 ) to 16.2 wt% ( C ∗ = 0.59 ). The solubility changes in KAS melts are interpreted to be due to the formation of strong complexes between Ti and K + in excess of that needed to charge balance Al 3+. The suggested stoichiometry of this complex is K 2Ti 2O 5 or K 2Ti 3O 7. In CAS melts, the data suggest that Ca 2+ in excess of A1 3+ is not as effective at complexing with Ti as is K +. The greater solubility of rutile in CAS melts when C ∗ is less than 0.54 compared to KAS melts of equal K ∗ ratio results primarily from competition between Ti and Al for complexing cations (Ca vs. K). TiK β x-ray emission spectra of KAS glasses ( K ∗ = 0.43-0.60 ) with 7 mole% added TiO 2, rutile, and Ba 2TiO 4, demonstrate that the average Ti-O bond length in these glasses is equal to that of rutile rather than Ba 2TiO 4, implying that Ti in these compositions is 6-fold rather than 4-fold coordinated. Re-examination of published spectroscopic data in light of these results and the solubility data, suggests that the 6-fold coordination polyhedron of Ti is highly distorted, with at least one Ti-O bond grossly undersatisfied in terms of Pauling's rules.

  4. Polyamide-layered silicate nanocomposites by melt processing

    NASA Astrophysics Data System (ADS)

    Fornes, Timothy Dean

    Polyamide-layered silicate nanocomposites based on nylon 6, 11, and 12 and organically modified montmorillonites (organoclay) were prepared by twin screw extrusion. Carefully designed component structure-nanocomposite morphology and property investigations on these materials were executed to understand why nylon 6 readily exfoliates organoclay. The polyamide structure strongly influences the extent of clay platelet delamination and level of property enhancement, as determined by X-ray, transmission electron microscopy and stress-strain analyses. High molecular weight nylon 6 materials lead to better organoclay exfoliation and greater nanocomposite moduli and yield strengths than lower molecular weight materials; this is attributed to higher levels of shear stress imparted on the clay by the higher viscosity polymer. The ratio of amide to methylene units in the repeat structure of nylon 6 appears to affect the polymer-organoclay affinity since a large increase in aliphatic content, i.e., nylon 6 versus nylon 12, results in less organoclay dispersion and lower reinforcing efficiency. The structure of the organoclay is also critical for producing well-exfoliated nylon 6 nanocomposites. Alkyl ammonium surfactants that cover less montmorillonite surface in the organoclay are more effective at exfoliating clay and generating improved nanocomposite stiffness and strength; such surfactants facilitate more desirable polyamide-silicate interactions, yet maintain sufficient organoclay gallery spacings needed both to overcome the cohesive forces between neighboring platelets and to facilitate polymer intercalation. The source of sodium montmorillonite used to form the organoclay is also important. The superior properties observed in nylon 6 nanocomposites may be explained by conventional ideas of reinforcement as predicted by composite theories like those of Halpin-Tsai or Mori-Tanaka. Based on good agreement between experimental nanocomposite moduli and model predictions it

  5. Density of Hydrous Ultramafic Silicate Melt under the Earth's Deep Upper Mantle Conditions

    NASA Astrophysics Data System (ADS)

    Jing, Z.; Matsukage, K. N.; Karato, S.

    2005-12-01

    Density of silicate melts is a critical material property in our understanding of geochemical evolution of the Earth. Previous studies (e.g., Agee & Walker 1993; Suzuki et al., 1995) showed that the density of dry silicate melts can be higher than that of surrounding solids under deep upper mantle conditions. However, melts formed under such conditions likely contain some water (Bercovici & Karato, 2003), which will reduce the melt density. In this study, we performed sink/float experiments between 10 and 14GPa and at 2173K to determine the density of hydrous ultramafic silicate melts, using a Kawai-type multianvil apparatus. We choose a target melt composition based on the experimental study by Litasov & Ohtani (2002). With this chemical composition, olivine reacts with the melt above the liquidus, so we used diamond as the density marker. However, diamond is much denser than a melt with a typical mantle like Fe/Mg ratio. Therefore in this study we determined the density of melts with high Fe contents, and from the relation between Fe content and melt density, we inferred the melt density with Earth-like Fe/Mg. Four Fe-rich compositions with 5wt% water and different iron content were chosen as starting materials. Density crossovers between melts and diamond were observed for all compositions. The densities of four melts at 14GPa and 2173K were calculated using the Birch-Murnaghan equation of state. The pressure derivative of isothermal bulk modulus (Kt') of the melts was estimated to be around 4. The density of mantle melt with mantle value of content and 5wt% water at 14GPa, 2173K was extrapolated to be ~3.42±0.4g/cm3. We compared our density results for hydrous melts with previous results on dry melts and found that water is more compressible than other components in melt. The estimated partial molar volume of water at 14GPa and 2173K is ~8±2cm3/mol, which is significantly lower than the value at low pressures. The conditions under which the density crossover

  6. Nanoscale Origin of the Dichotimous Viscosity-Pressure Behavior in Silicate Melts

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Sakamaki, T.; Skiner, L.; Jing, Z.; Yu, T.; Kono, Y.; Park, C.; Shen, G.; Rivers, M. L.; Sutton, S. R.

    2013-12-01

    A defining characteristic of silicate melts is the degree of polymerization (tetrahedral connectivity), which dictates physical properties such as viscosity and density. While viscosity of depolymerized silicate melts increases with pressure consistent with free volume theory, isothermal viscosity of polymerized melts decreases with pressure up to ~3 - 5 GPa, above which it turns over to normal (positive) pressure dependence. We conducted high-pressure melt structure studies along the jadeite (Jd) - diopside (Di) join, using a Paris-Edinburgh Press at the HPCAT beamline 16-BM-B and measured Jd melt density using a DIA type apparatus based on x-ray absorption at GSECARS beamline 13-BM-D. Structures of polymerized (Jd and Jd50Di50) and depolymerized (Di) melts show distinct responses to pressure. For Jd melt, T-O, T-T bond lengths (where T denotes tetrahedrally coordinated Al and Si) and T-O-T angle all exhibit rapid, sometimes non-linear decrease with increasing pressure to ~3 GPa. For Di melt, these parameters vary linearly with pressure and change very little. Molecular dynamics calculations, constrained by the x-ray structural data, were employed to examine details of structural evolution in polymerized and depolymerized liquids. A structural model is developed to link structural evolution to changes in melt properties, such as density and viscosity, with pressure. We show that the pressure of the viscosity turnover corresponds to the tetrahedral packing limit, below which the structure is compressed through tightening of the inter-tetrahedral bond angle, resulting in continual breakup of tetrahedral connectivity and viscosity decrease. Above the turnover pressure, Si and Al coordination increases to allow further packing, with increasing viscosity. This structural response prescribes the distribution of melt viscosity and density with depth, and may be the main controlling factor for magma transport rates in terrestrial planetary interiors.

  7. Glass Forming Ability of Sub-Alkaline Silicate Melts

    NASA Astrophysics Data System (ADS)

    Vetere, F. P.; Iezzi, G.; Behrens, H.; Holtz, F.; Ventura, G.; Misiti, V.; Mollo, S.; Perugini, D.

    2014-12-01

    The glass forming ability (GFA) and critical cooling rate (Rc) of six natural sub-alkaline melts from basalt to rhyolite (i.e., B100, B80R20, B60R40, B40R60, B20R80, and R100) have been quantified through cooling-induced solidification experiments of 9000, 1800, 180, 60, 7 and 1 °C/h conducted at ambient pressure and air buffering conditions, in a temperature range between 1300 °C (superliquidus region) and 800 °C (glass transition region), The phase proportion in each run-product was determined by image analysis on about 500 BS-SEM microphotographs. The phase assemblage consists of glass, clinopyroxene, spinel, and plagioclase with the occurrence of sporadic olivine, orthopyroxene and melilite. Both the glass and crystalline fractions are well correlated with the composition of residual melt. Generally, the amount of crystals decreases with increasing cooling rate. However, some exceptions occurs showing no correlations or even opposite trends. For the example of, Al2O3 and CaO in clinopyroxenes from B100, B80R20, B60R40 and B40R60, their concentrations scale as a function of both cooling rate and the degree of clinopyroxene crystallization. The value of Rc changes of 5 order of magnitude from <1 to ~9000 °C/h when the melt composition changes from R100 to B100, respectively. The most important Rc variations are measured between B80R20 and B60R40, levelling off towards B100. This trend scales with NBO/T (non bridging oxygen per tetrahedron) and can be modelled by the following master sigmoid equation: Rc = a / 1+e-(NBO/T-xo/b), where a, b and xo are fitting parameters equal to 9214, 0.040 and 0.297, respectively. Our data can be used to retrieve the solidification conditions of aphyric, degassed and oxidised lavas. Indeed, the relationship between crystal content and cooling kinetics suggests that the solidification path is more complex than previously assumed and strongly non-linear. This finding has also implications to design glass-ceramics based on natural

  8. Compositional effect on the pressure derivatives of bulk modulus of silicate melts

    NASA Astrophysics Data System (ADS)

    Jing, Zhicheng; Karato, Shun-ichiro

    2008-07-01

    Although the bulk moduli ( KT0) of silicate melts have a relatively narrow range of values, the pressure derivatives of the isothermal bulk modulus ( KT0') can assume a broad range of values and have an important influence on the compositional dependence of the melt compressibility at high pressure. Based on the melt density data from sink/float experiments at high pressures in the literature, we calculate KT0' using an isothermal equation of state (EOS) (e.g., Birch-Murnaghan EOS and Vinet EOS) with the previously determined values of room-pressure density ( ρ0) and room-pressure bulk modulus ( KT0). The results show that best estimates of KT0' vary considerably from ~ 3 to ~ 7 for different compositions. KT0' is nearly independent of Mg # (molar Mg/(Mg + Fe)), but decreases with SiO 2 content. Hydrous melts have anomalously small KT0' leading to a high degree of compression at high pressures. For anhydrous melts, KT0' is ~ 7 for peridotitic melts, ~ 6 for picritic melts, ~ 5 for komatiitic melts, and ~ 4 for basaltic melts.

  9. Carbon Dissolution in Reduced Silicate and Alloy Melts - a Frontier for Understanding Evolution of Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Dasgupta, R.; Chi, H.; Li, Y.; Duncan, M. S.; Tsuno, K.

    2014-12-01

    C-O-H-S-N volatile elements sequestration in and release from silicate and metallic melts are key in controlling the planet scale distribution of these elements and thus are critical for thermo-chemical and dynamic evolution of terrestrial planets. To understand the distribution of carbon during accretion, core formation, magma ocean crystallization, and ongoing evolution of reduced mantles domains such as those of Mars, the Moon, and deep Earth, carbon chemistry in reduced silicates and alloys must be constrained, but currently are poorly known. Here we summarize recent experimental efforts to (1) constrain the speciation and solubility of carbon in graphite-saturated natural mafic melts at fO2 below IW buffer and (2) C solubility in Fe-Ni-rich alloy melts. Quenched glasses and alloys generated to 8 GPa and 2200 °C are analyzed using a combination of electron and ion microprobe, FTIR, and Raman spectroscopy. Dissolved carbonates and bulk C solubility (<200 ppm) of graphite-saturated silicate glasses are observed to increase with decreasing pressure and increasing temperature, melt depolymerization index (e.g., NBO/T), and fO2 from ~IW-1.5 to IW [1,2]. Over the range in fO2, melt H2O content also mildly enhances carbonate dissolution, likely in part owing to the depolymerizing effect of H2O in the melt. At fO2>IW-1.5, dissolved C is a mixture of carbonates and other species, but below ~IW-1.5 the carbonate doublet is undetectable in IR spectra, with Raman spectra indicating the dominant species being methane or other methyl groups. In addition, with diminishing fO2 from IW-2 to IW-5, C solubility trend reverses, i.e., it increases with decreasing fO2 and also shows a much stronger dependence on melt H content [3], consistent with the enhanced solubility of methane in silicate melt with decreasing fO2 and increasing with square of fH2. However, Fe-Ni-rich alloy melts have high C solubility (~0.7-7 wt.%) that diminishes mostly with increasing Ni, Si, and S contents

  10. Entropy and structure of silicate glasses and melts

    USGS Publications Warehouse

    Richet, P.; Robie, R.A.; Hemingway, B.S.

    1993-01-01

    Low-temperature adiabatic Cp measurements have been made on NaAlSi2O6, MgSiO3, Ca3Al2Si3O12 and Ca1.5Mg1.5Al2Si3O12 glasses. Above about 50 K, these and previous data show that the heat capacity is an additive function of composition to within ??1% throughout the investigated glassforming part of the system CaO-MgO-Al2O3-SiO2. In view of the determining role of oxygen coordination polyhedra on the low-temperature entropy, this is interpreted as indicating that Si and Al are tetrahedrally coordinated in all these glasses, in agreement with structural data; whereas Ca and Mg remain octahedrally coordinated. In contrast, heat capacities and entropies are not additive functions of composition for alkali aluminosilicates, indicating increases in the coordination numbers of alkali elements from about six to nine when alumina is introduced. A thermochemical consequence of additivity of vibrational entropies of glasses is that entropies of mixing are essentially configurational for calcium and magnesium aluminosilicate melts. For alkali-bearing liquids, it is probable that vibrational entropies contribute significantly to entropies of mixing. At very low temperatures, the additive nature of the heat capacity with composition is less well followed, likely as a result of specific differences in medium-range order. ?? 1993.

  11. Hydrogen-alkali exchange between silicate melts and two-phase aqueous mixtures: an experimental investigation

    NASA Astrophysics Data System (ADS)

    Williams, Thomas J.; Candela, Philip A.; Piccoli, Philip M.

    Experiments were performed in the three-phase system high-silica rhyolite melt + low-salinity aqueous vapor + hydrosaline brine, to investigate the exchange equilibria for hydrogen, potassium, and sodium in magmatic-hydrothermal systems at 800 °C and 100 MPa, and 850 °C and 50 MPa. The Kaqm/meltH,Na and Kaqm/meltH,K for hydrogen-sodium exchange between a vapor + brine mixture and a silicate melt are inversely proportional to the total chloride concentration (ΣCl) in the vapor + brine mixture indicating that HCl/NaCl and HCl/KCl are higher in the low-salinity aqueous vapor relative to high-salinity brine. The equilibrium constants for vapor/melt and brine/melt exchange were extracted from regressions of Kaqm/meltH,Na and Kaqm/meltH,K versus the proportion of aqueous vapor relative to brine in the aqueous mixture (Faqv) at P and T, expressed as a function of ΣCl. No significant pressure effect on the empirically determined exchange constants was observed for the range of pressures investigated. Model equilibrium constants are: Kaqv/meltH,Na(vapor/melt)=26(+/-1.3) at 100 MPa (800 °C), and 19( +/- 7.0) at 50 MPa (850 °C) Kaqv/meltH,K=14(+/-1.1) at 100 MPa (800 °C), and 24(+/-12) at 50 MPa (850 °C) Kaqb/meltH,b(brine/melt)= 1.6(+/-0.7) at 100 MPa (800 °C), and 3.9(+/-2.3) at 50 MPa (850 °C) and Kaqb/meltH,K=2.7(+/-1.2) at 100 MPa (800 °C) and 3.8(+/-2.3) at 50 MPa (850 °C). Values for Kaqv/meltH,K and Kaqb/meltH,K were used to calculate KCl/HCl in the aqueous vapor and brine as a function of melt aluminum saturation index (ASI: molar Al2O3/(K2O+Na2O+CaO) and pressure. The model log KCl/HCl values show that a change in melt ASI from peraluminous (ASI = 1.04) to moderately metaluminous (ASI = 1.01) shifts the cooling pathway (in temperature-log KCl/HCl space) of the aqueous vapor toward the andalusite+muscovite+K-feldspar reaction point.

  12. Silicate melt inclusions and glasses in lunar soil fragments from the Luna 16 core sample

    USGS Publications Warehouse

    Roedder, E.; Weiblen, P.W.

    1972-01-01

    More than 2000 fragments were studied microscopically, and electron microprobe analyses were made of 39 selected areas, from a few square mm of polished surface, through 75- to 425-??m fragments of lunar soil from two samples of the Luna 16 core. The silicate melt inclusions and glasses differ in important details from those observed earlier in the Apollo samples. Melt inclusions in olivine contain epitaxially oriented daughter crystals, but also show a similar epitaxy around the outside of the crystals not observed in previous lunar samples. Melt inclusions in ilmenite suggest trapping at successive stages in a differentiation sequence. There is abundant evidence for late-stage silicate liquid immiscibility, with melt compositions similar but not identical to those from Apollo 11 and 12. A comparison of the alkali ratio of any given bulk rock analysis with that of its late-stage, high-silica melt shows gross differences for different rocks. This is pertinent to understanding late-stage differentiation processes. Glass fragments and spherules exhibit a wide range of crystallization textures, reflecting their wide range of compositions and cooling histories. No significant differences were found between the two portions of core examined (Zones A and D). ?? 1972.

  13. Molybdenum Valence in Basaltic Silicate Melts: Effects of Temperature and Pressure

    NASA Technical Reports Server (NTRS)

    Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Choi, Y.; Pando, K.

    2011-01-01

    The metal-silicate partitioning behavior of molybdenum has been used as a test for equilibrium core formation hypotheses [for example, 1-6]. However, current models that apply experimental data to equilibrium core-mantle differentiation infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Molybdenum, a multi-valent element with a valence transition near the fO2 of interest for core formation (approx.IW-2) will be sensitive to changes in fO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo(6+) can be either octahedrally or tetrahedrally coordinated. Here we present X-ray absorption near edge structure (XANES) measurements of Mo valence in basaltic run products at a range of P, T, and fO2 and further quantify the valence transition of Mo.

  14. Velocity of a freely rising gas bubble in a soda-lime silicate glass melt

    NASA Technical Reports Server (NTRS)

    Hornyak, E. J.; Weinberg, M. C.

    1984-01-01

    A comparison is conducted between measured velocities for the buoyant rise of single bubbles of varying size and composition, in a soda-lime silicate glass melt, with the steady state velocities predicted by the Stokes and Hadamard-Rybczynski formulas. In all cases, the data are noted to fit the Hadamard-Rybczynski expression for steady state rise speed considerably better than the Stokes formula.

  15. A partial molar volume for ZnO in silicate melts.

    NASA Astrophysics Data System (ADS)

    Ledda, B.; Potuzak, M.; Dingwell, D. B.; Courtial, P.

    2004-12-01

    Trace elements in igneous petrology have, in comparison with major elements, a relevance in the petrogenetic modelling of magmatic differentiation that far outweighs their relative abundance. Optimal use of the information contained in trace element variations within igneous phases requires an accurate description of their partitioning behaviour as a function of phase composition and structure, as well as temperature and pressure. In this manner, the partial molar thermodynamic properties of trace elements in silicate melts may contribute to the petrogenetic modelling of such systems. With this in mind, a series of investigations into the partial molar properties of trace elements in silicate melts have been carried out in recent years. Here we extend this work to the analysis of the volumetric properties of ZnO in silicate melts. Densities of 8 Zn-bearing silicate melts have been determined in air in the temperature range of 1363 to 1850 K. The compositional joins investigated (sodium disilicate (NS2) - ZnO; anorthite-diopside 1 bar eutectic (AnDi) - ZnO; and diopside - petedunnite) were chosen based on the pre-existing experimental density data set, their petrological relevance and to provide a test for significant compositionally induced variations in the structural role of ZnO. The ZnO concentrations investigated range up to 25 mol% for sodium disilicate, 20 mol% for the anorthite-diopside 1 atm eutectic and 100 mol% petedunnite. Molar volumes and expansivities of all melts have been derived. The molar volumes of the present liquids all decrease with increasing ZnO content. The partial molar volume of ZnO derived here from the volumetric measurements for each binary system is the same within error. A multicomponent fit to the volumetric data for all compositions yields a value of 14.141(0.730) cm3.mol-1 at 1300 K. We find, herewith, no volumetric evidence for compositionally-induced coordination number variations for ZnO in alkali-bearing versus alkali

  16. Experimental investigations of influence of pressure on the solubility of sulfur in silicate melts.

    NASA Astrophysics Data System (ADS)

    Kostyuk, Anastasia; Gorbachev, Nikolay

    2010-05-01

    Sulfide-silicate demixing of silicate melts on immiscible silicate and sulfide liquids occurs at magma sulfur saturation. This type of liquation plays an important role in geochemistry of mantle magmas, in processes of magmatic differentiation, and in ore deposit formation. The major parameter defining sulfide-silicate stratification of silicate melts is solubility of sulfur in magmas. It is considered that «solubility of sulfur» is concentration of sulfur in silicate melts. The previous researches have established positive dependence of solubility of sulphur on temperature [1, 2], melt composition [3, 4], oxidation-reduction conditions [5, 6] and our experimental data confirm it. However, available data does not give a simple answer about dependence of solubility of sulfur from pressure in modelling and natural "dry" sulfide-saturated silicate melts. The reason of difference in experiments remains not clear and further work is needed on this topic. In this paper, we report our findings on the influence of pressure on the solubility of sulfur in hydrous magnesian melts. This melts are represent by olivine basalt - picrite, coexisting with Fe-Cu-Ni sulfide melt and harzburgite (Ol+Opx) and it was investigated in a temperature range from 1200 to 1350°С and a pressure range from 0.2 to 2.5 GPa. Experiments were carried out on the piston-cylinder at Р=1-2.5GPa and in an internal-heated pressure vessels at P=0.2-0.6 GPa by a quenching technique. Our findings disagree with all previous studies demonstrating the positive [7] or negative [8, 9] influence of pressure on the solubility of sulfur in silicate melts. Our researches have shown complicated influence of pressure. Concentration of sulfur in glasses increases with increase in pressure from 0.2 to 0.6 GPa in experiments where andesite was used as a starting material. The sulfur concentration increases from 0.09 wt.% at 0.2 GPa to 0.4 wt.% at 0.6 GPa and Т=1200°С. In hydrous magnesian basalts (12-18 % MgO), we

  17. Evolution of melt-vapor surface tension in silicic volcanic systems: Experiments with hydrous melts

    USGS Publications Warehouse

    Mangan, M.; Sisson, T.

    2005-01-01

    We evaluate the melt-vapor surface tension (??) of natural, water-saturated dacite melt at 200 MPa, 950-1055??C, and 4.8-5.7 wt % H2O. We experimentally determine the critical supersaturation pressure for bubble nucleation as a function of dissolved water and then solve for ?? at those conditions using classical nucleation theory. The solutions obtained give dacite melt-vapor surface tensions that vary inversely with dissolved water from 0.042 (??0.003) J m-2 at 5.7 wt% H2O to 0.060 (??0.007) J m-2 at 5.2 wt% H2O to 0.073 (??0.003) J m-2 at 4.8 wt% H2O. Combining our dacite results with data from published hydrous haplogranite and high-silica rhyolite experiments reveals that melt-vapor surface tension also varies inversely with the concentration of mafic melt components (e.g., CaO, FeOtotal, MgO). We develop a thermodynamic context for these observations in which melt-vapor surface tension is represented by a balance of work terms controlled by melt structure. Overall, our results suggest that cooling, crystallization, and vapor exsolution cause systematic changes in ?? that should be considered in dynamic modeling of magmatic processes.

  18. Experimental correlation of melt structures, nucleation rates, and thermal histories of silicate melts

    NASA Technical Reports Server (NTRS)

    Boynton, W. V.; DRAKE; HILDEBRAND; JONES; LEWIS; TREIMAN; WARK

    1987-01-01

    The theory and measurement of the structure of liquids is an important aspect of modern metallurgy and igneous petrology. Liquid structure exerts strong controls on both the types of crystals that may precipitate from melts and on the chemical composition of those crystals. An interesting aspect of melt structure studies is the problem of melt memories; that is, a melt can retain a memory of previous thermal history. This memory can influence both nucleation behavior and crystal composition. This melt memory may be characterized quantitatively with techniques such as Raman, infrared and NMR spectroscopy to provide information on short-range structure. Melt structure studies at high temperature will take advantage of the microgravity conditions of the Space Station to perform containerless experiments. Melt structure determinations at high temperature (experiments that are greatly facilitated by containerless technology) will provide invaluable information for materials science, glass technology, and geochemistry. In conjunction with studies of nucleation behavior and nucleation rates, information relevant to nucleation in magma chambers in terrestrial planets will be acquired.

  19. In-situ determination of the oxidation state of iron in Fe-bearing silicate melts

    NASA Astrophysics Data System (ADS)

    Courtial, P.; Wilke, M.; Potuzak, M.; Dingwell, D. B.

    2005-12-01

    Terrestrial lavas commonly contain up to 10 wt% of iron. Furthermore, rocks returned from the Moon indicate lunar lava containing up to 25 wt% of iron and planetary scientists estimated that the martian mantle has about 18 wt% of iron. An experimental challenge in dealing with Fe-bearing silicate melts is that the oxidation state, controlling the proportions of ferric and ferrous iron, is a function of composition, oxygen fugacity and temperature and may vary significantly. Further complications concerning iron originate from its potential to be either four-, six- or even five-fold coordinated in both valence states. Therefore, the oxidation state of iron was determined in air for various Fe-bearing silicate melts. Investigated samples were Na-disilicate (NS), one atmosphere anorthite-diopside eutectic (AD) and haplogranitic (HPG8) melts containing up to 20, 20 and 10 wt% of iron, respectively. XANES spectra at the Fe K-edge were collected for all the melts at beamline A1, HASYLAB, Hamburg, using a Si(111) 4-crystal monochromator. Spectra were collected for temperatures up to 1573 K using a Pt-Rh loop as heating device. The Fe oxidation state was determined from the centroid position of the pre-edge feature using the calibration of Wilke et al. (2004). XANES results suggest that oxidation state of iron does not change within error for NS melts with addition of Fe, while AD and HPG8 melts become more oxidised with increasing iron content. Furthermore, NS melts are well more oxidised than AD and HPG8 melts that exhibit relatively similar oxidation states for identical iron contents. The oxidation state of iron for NS melts appears to be slightly temperature-dependent within the temperature range investigated (1073-1573 K). However, this trend is stronger for AD and HPG8 melts. Assuming that glass reflects a picture of the homogeneous equilibria of the melt, the present in-situ Fe-oxidation states determined for these melts were compared to those obtained on quenched

  20. Liquid immiscibility between silicate, carbonate and sulfide melts in melt inclusions hosted in co-precipitated minerals from Kerimasi volcano (Tanzania): evolution of carbonated nephelinitic magma

    NASA Astrophysics Data System (ADS)

    Guzmics, Tibor; Mitchell, Roger H.; Szabó, Csaba; Berkesi, Márta; Milke, Ralf; Ratter, Kitti

    2012-07-01

    The evolution of a carbonated nephelinitic magma can be followed by the study of a statistically significant number of melt inclusions, entrapped in co-precipitated perovskite, nepheline and magnetite in a clinopyroxene- and nepheline-rich rock (afrikandite) from Kerimasi volcano (Tanzania). Temperatures are estimated to be 1,100°C for the early stage of the melt evolution of the magma, which formed the rock. During evolution, the magma became enriched in CaO, depleted in SiO2 and Al2O3, resulting in immiscibility at ~1,050°C and crustal pressures (0.5-1 GPa) with the formation of three fluid-saturated melts: an alkali- and MgO-bearing, CaO- and FeO-rich silicate melt; an alkali- and F-bearing, CaO- and P2O5-rich carbonate melt; and a Cu-Fe sulfide melt. The sulfide and the carbonate melt could be physically separated from their silicate parent and form a Cu-Fe-S ore and a carbonatite rock. The separated carbonate melt could initially crystallize calciocarbonatite and ultimately become alkali rich in composition and similar to natrocarbonatite, demonstrating an evolution from nephelinite to natrocarbonatite through Ca-rich carbonatite magma. The distribution of major elements between perovskite-hosted coexisting immiscible silicate and carbonate melts shows strong partitioning of Ca, P and F relative to FeT, Si, Al, Mn, Ti and Mg in the carbonate melt, suggesting that immiscibility occurred at crustal pressures and plays a significant role in explaining the dominance of calciocarbonatites (sövites) relative to dolomitic or sideritic carbonatites. Our data suggest that Cu-Fe-S compositions are characteristic of immiscible sulfide melts originating from the parental silicate melts of alkaline silicate-carbonatite complexes.

  1. Solubility of Au in Cl- and S-bearing hydrous silicate melts

    NASA Astrophysics Data System (ADS)

    Botcharnikov, R. E.; Linnen, R. L.; Holtz, F.

    2010-04-01

    The solubility of Au in Cl- and S-bearing hydrous rhyodacitic and andesitic melts has been experimentally investigated at 1050 °C, 200 MPa and log fO 2 close to the Ni/NiO solid oxygen buffer (NNO). The concentrations of Au in the experimental glasses have been determined using Laser Ablation ICP-MS (LA) with special efforts to avoid incorporation of Au micronuggets in the analysis. It is concluded that metal micronuggets are an experimental artefact and produced by Au partitioning into the fluids during heating with consequent precipitation on fluid dissolution in the melting glass powder. Hence, the micronuggets do not represent quench phases and must be excluded from the analysis. The micro-analytical data obtained by LA show that Au concentrations vary from ˜0.2 to ˜2.5 ppm by weight, generally consistent with the literature data for other melt compositions. The measured Au concentrations increase with increasing amounts of Cl and S dissolved in the silicate melt and show a correlation with the apparent activities of Cl and S in the system. The apparent activities of Cl and S are defined by the simplified linear relationship between volatile concentrations in the melt and activity of volatiles. The maximum activity ( a∗ = 1) is assumed to be reached at the saturation of the systems in respect of Cl-rich brine or FeS liquid for Cl and S, respectively. The dependence of Au solubility on the concentrations/activities of Cl and S at the fixed redox conditions shows that Au may form not only oxide- but also Cl- and S-bearing complexes in silicate melts. Furthermore, it indicates that exsolution of S and Cl from the melt by degassing/segregation/crystallization processes may lead to mobilization and extraction of Au into the fluid, liquid and/or mineral phase(s).

  2. Structure and Viscosity of Carbonate-Silicate Melts Using in situ Techniques

    NASA Astrophysics Data System (ADS)

    Hummer, D. R.; Manning, C. E.; Kavner, A.; Kono, Y.; Park, C.; Kenney-Benson, C.

    2015-12-01

    The chemical properties of carbon-rich magmas at high pressures and temperatures are a major factor controlling the deep-Earth carbon cycle, and may play a crucial role in global magmatism at depth. We have measured the structure of carbonate-silicate liquids as a function of carbon content along the calcite-wollastonite (CaCO3-CaSiO3) and calcite-forsterite (CaCO3-Mg2SiO3) compositional joins at ~1800 oC, and 3 or 6 GPa in a Paris-Edinburgh press using X-ray diffuse scattering. Pair distribution functions calculated from the scattering data confirm that CaCO3 behaves as an ionic liquid, while compositions with 40-100 wt% wollastonite contain polymerized silicate with an average connectivity (Qn) of at least two bridging O per Si (Q2). Even liquid compositions with as little as 35 wt% forsterite component contain silicate polymers, despite the absence of bridging O in the crystalline orthosilicate. As the carbonate content of the melt is increased, the average connectivity of SiO4 units linearly increases from ~Q2 for pure wollastonite liquid to >Q3 for 40 wt% wollastonite, even though less silicate is present. Analysis of Ca-Ca and Ca-Si pair correlations, as well as Ca-O bond distances, indicate that Ca2+ bonds more strongly to the silicate framework as carbonate content increases. Increasing pressure from 3 to 6 GPa at constant composition causes Qn to fall near Q0. The trends in local atomic structure with composition and pressure explain falling sphere viscometry measurements in carbonate-silicate liquids at upper mantle conditions. These viscosities are as low as 6x10-3 Pa-s for pure CaCO3, only half a log unit higher than that of water, and span ~1.6 log units between the carbonate and silicate end-members. Structural and viscosity trends taken together indicate carbonate-rich, depolymerized and highly mobile liquid at depth which transitions into silicate-rich, polymerized and much less mobile liquid as the melt ascends into the crust.

  3. Metal/Silicate Partitioning, Melt Speciation, Accretion, and Core Formation in the Earth

    NASA Astrophysics Data System (ADS)

    Drake, M. J.; Hillgren, V. J.; Dearo, J. A.; Capobianco, C. J.

    1993-07-01

    Core formation in terrestrial planets was concomitant with accretion. Siderophile and chalcophile element signatures in the mantles of planets are the result of these processes. For Earth, abundances of most siderophile and chalcophile elements are elevated relative to predictions from simple metal/silicate equilibria at low pressures [1]. This observation has led to three hypotheses for how these abundances were established: heterogeneous accretion [2], inefficient core formation [3], and metal/silicate equilibria at magma ocean pressures and temperatures [4]. Knowledge of speciation of siderophile elements in silicate melts in equilibrium with metal may help distinguish between these hypotheses. But there is some uncertainty regarding speciation. For example, Ni and Co have been reported to be present as 1+ or zero valence species in silicate melts at redox states appropriate to planetary accretion, rather than the expected 2+ state [5-7]. Independent metal/silicate partitioning experiments by three members of this group using two different experimental designs on both synthetic and natural compositions do not show evidence for Ni and Co in valence states other than 2+ over a wide range of redox states. For example, solid metal/silicate melt partition coefficients for Ni at 1260 degrees C obtained by VJH from experiments investigating the partitioning of Ni, Co, Mo, W, and P are indistinguishable from those obtained by JAD in similar experiments investigating the partitioning of Ni, Ge, and Sn. Both datasets define a line with the equation: log D(Ni) = - 0.54log fO2 - 3.14 with r^2 > 0.995. (Note that fO2 was calculated in both studies from thermodynamic data and phase compositions. A small, systematic offset from the true fO2 as measured by a solid electrolyte cell affects both equations similarly, but does not diminish their close agreement.) The valence of Ni in the silicate melt is obtained by multiplying the slope of the line by -4, indicating divalent Ni in

  4. The role of Iron on the dissolution of Sulfur in hydrous silicate melts

    NASA Astrophysics Data System (ADS)

    Klimm, K.; Kohn, S. C.; Botcharnikov, R. E.

    2012-04-01

    It is well established that the sulfur solubility in silicate melts is a function of fO2 and melt compositions [1]. At high fO2, S6+ is dominant and more soluble in natural silicate melts than S2-, which is dominant at low fO2. Primitive melt compositions such as basalt can contain an order of magnitude more sulfur than more evolved melt compositions such as rhyolite. The compositional control on the sulfur solubility is yet not fully understood but a positive correlation with FeO has often been observed. Thus, determining the S2-- and S6+-speciesincorporated in the silicate glass structure is crucial to unravel the sulfur dissolution mechanism in silicate melts. Together with solubility measurements such information is essential to quantify the sulfide and sulfate capacity of silicate melts and to understand the sulfur flux in subduction zones. Here we present Raman and XANES measurements on experimentally equilibrated sulfur-bearing, hydrous silicate glasses, including soda-lime (SLG), K2Si4O9 (KSG), albite and trondhjemite (TROND) compositions. A series of SLG and KSG glasses, doped with small quantities of Fe, were also studied in order to determine the effect of Fe/S on the S solubility. The experiments were performed in internally heated and cold seal pressure vessels at 200 MPa, 1000 and 850 ° C and fO2 ranging from logfO2 = QFM-2.4 to QFM+4. The systematic correlation of features in Raman and XANES spectra allows the identification of at least four different S-species in the glasses depending on fO2 and Fe/S of the system. In Fe-free melts S is dissolved as SH-, H2S and/or SO42- depending on the prevailing fO2. S2- is more soluble than S6+.The total sulfur solubility depends on the degree of polymerisation of the melt and increases with increasing NBO/T. This correlation is much more pronounced for SH- and H2S than for SO42-. Adding Fe results in the formation of Fe-S-complexes at the expense of SH- and H2S, which are still observed up to Fe/S ~ 2.6. The S

  5. Elastic properties of silicate melts at high pressure and implications for low velocity anomalies in the crust and mantle

    NASA Astrophysics Data System (ADS)

    Clark, A. N.; Lesher, C. E.

    2015-12-01

    Regions of low seismic velocities in the mantle and crust are commonly attributed to the presence of silicate melt or aqueous fluid. The elastic properties of silicate melts are typically modeled at high pressure using equations of state developed for crystalline materials. However, amorphous silicates spanning a wide range of composition and structure, i.e. SiO2 to MgSiO3, and including naturally occurring basalt compositions, exhibit a weak dependence of P-wave velocity on density in clear violation of Birch's law, which governs the behavior of crystalline materials. This anomalous behavior is attributed to the high degree of flexibility of the silicate network on loading that may be a general property of naturally occurring silicate melts at crustal and upper mantle conditions. If this is the case, P-wave velocities for silicate melts will be significantly less pressure dependent than previously assumed, which in turn will enhance the effects of melt fraction on lowering aggregate mantle seismic velocities. Here we present VP calculated for partially molten mantle up to 20 GPa showing that melt fractions purported to explain VP reductions associated with the lithosphere-asthenosphere boundary may be overestimated by 15%, while those reported for the transition zone may be overestimated to an even greater extent. Moreover, we predict that d lnVS/d lnVP (RSP) should vary little across low velocities regions within the upper mantle due solely to the presence of melt, but will be strongly influenced by how melt is distributed, consistent the work of [1]. Finally, RSP is found to be relatively insensitive to type of fluid present, contrary to conventional wisdom, and thus caution is warranted in attributing changes in RSP to either silicate melt or aqueous fluids. The implications of these findings for interpreting low velocity anomalies beneath hotspots and arcs (e.g. Iceland and Japan) will be discussed. [1] Takei, Y. (2002) JGR vol. 107

  6. Platinum partitioning between metal and silicate melts: Core formation, late veneer and the nanonuggets issue

    NASA Astrophysics Data System (ADS)

    Médard, Etienne; Schmidt, Max W.; Wälle, Markus; Keller, Nicole S.; Günther, Detlef

    2015-08-01

    High-pressure, high-temperature experiments have been performed at ∼1.2 GPa and 1360-2100 °C to investigate the partitioning of Pt between a silicate melt and a metallic melt. Our experiments indicate that nanonuggets encountered in previous experiments are experimental artifacts, formed at high temperature by oversaturation caused by high oxygen fugacity during the initial stages of an experiment. Experiments at high-acceleration using a centrifuging piston-cylinder show that nanonuggets can be removed by gravity during the experiment. Formation of nanonuggets can also be avoided by using initially reduced starting materials. The presence of iron is also a key element in reducing the formation of nanonuggets. Our nanonugget-free data are broadly consistent with previous nanonuggets-filtered data, and suggest that Pt partitioning becomes independent of oxygen fugacity below an oxygen fugacity of at least IW+2. Pt is thus possibly dissolved as a neutral species (or even an anionic species) at low fO2, instead of the more common Pt2+ species present at higher fO2. Due to low concentration, the nature of this species cannot be determined, but atomic Pt or Pt- are possible options. Under core-formation conditions, Pt partitioning between metal and silicate is mostly independent of oxygen fugacity, silicate melt composition, and pressure. Partition coefficient during core formation can be expressed by the following equation: log DPtMmetal/silicate = 1.0348 + 14698 / T (in weight units). Calculations indicate that the Pt content (and by extension the Highly Siderophile Elements content) of the Earth's mantle cannot be explained by equilibrium partitioning during core formation, requiring further addition of HSE to the mantle. The mass of this late veneer is approximately 0.4% of the total mass of the Earth (or 0.6% of the mass of the mantle).

  7. A computer simulation study of natural silicate melts. Part II: High pressure properties

    NASA Astrophysics Data System (ADS)

    Guillot, Bertrand; Sator, Nicolas

    2007-09-01

    The thermodynamic, structural and transport properties of natural silicate melts under pressure are investigated by molecular dynamics simulation with the help of a force field recently introduced by us [Guillot B. and Sator N. (2007) A computer simulation study of natural silicate melts. Part I: low pressure properties. Geochim. Cosmochim. Acta71, 1249-1265]. It is shown that the simulation reproduces accurately the bulk moduli of a large variety of silicate liquids as evaluated from ultrasonic studies. The equations of state (EOS) of the simulated melts are in good agreement with the density data on mid-ocean ridge basalt, komatiite, peridotite and fayalite as obtained either by sink/float experiments or by shock-wave compression. From the structural point of view it is shown that the population of [5]Al and [6]Al species increases rapidly upon initial compression (0-50 kbar) whereas for Si these highly coordinated species are found in a significant abundance (>5%) only above ˜50 kbar for [5]Si and ˜100-150 kbar for [6]Si. This increase of the coordination of network formers is not the only response of the melt structure to the densification: there is also a large redistribution of the T-O-T (T = Si, Al) bond angles with the pressure and noticeably upon initial compression in rhyolitic and basaltic liquids. Furthermore, a detailed analysis of the population of bridging oxygens (BO) and nonbridging oxygens (NBO) points out that the polymerization of the melt generally increases when the pressure increases, the magnitude of this polymerization enhancement being all the more important that the melt is depolymerized at low pressure. The role of triclusters (threefold coordinated oxygens to network former cations) is particularly emphasized in acidic and basaltic liquids. The pressure-induced redistribution of the oxygen atoms through the melt structure is also stressed. Finally, the simulation predicts a nonmonotonic behavior of the diffusivity of network former

  8. An electrochemical series of redox couples in silicate melts - A review and applications to geochemistry

    NASA Technical Reports Server (NTRS)

    Schreiber, Henry D.

    1987-01-01

    An electrochemical series for redox couples in a glass-forming oxide melt is developed. This series is a quantitative numerical scale of reference reduction potentials of the redox couples in a silicate melt that is a model for basaltic magmas. The redox couples are ordered in terms of their reference reduction potentials; the order appears to be relatively independent of the exact melt composition and temperature. Thus, upon calibration to a desired composition, oxygen fugacity, and temperature, this electrochemical series can provide estimates of redox state proportions in basaltic magmas on different planetary bodies. The geochemical electrochemical series can also be used to understand the interrelationship of the redox state of the magma and the presence of volatile species such as oxygen, water, sulfur gases, and carbon gases.

  9. Mutual interactions of redox couples via electron exchange in silicate melts - Models for geochemical melt systems

    NASA Technical Reports Server (NTRS)

    Schreiber, Henry D.; Merkel, Robert C., Jr.; Schreiber, V. Lea; Balazs, G. Bryan

    1987-01-01

    The mutual interactions via electron exchange of redox couples in glass-forming melts were investigated both theoretically and experimentally. A thermodynamic approach for considering the mutual interactions leads to conclusion that the degree of mutual interaction in the melt should be proportional in part to the difference in relative reduction potentials of the interacting redox couples. Experimental studies verify this conclusion for numerous redox couples in several composition/temperature/oxygen fugacity regimes. Geochemical systems simultaneously possess many potentially multivalent elements; the stabilized redox states in the resulting magmas can be explained in part by mutual interactions and by redox buffering through the central Fe(III)- Fe(II) couples in the melts. The significance of these results for basaltic magmas of the earth, moon, and meteorites is addressed.

  10. Zircon saturation in silicate melts: a new and improved model for aluminous and alkaline melts

    NASA Astrophysics Data System (ADS)

    Gervasoni, Fernanda; Klemme, Stephan; Rocha-Júnior, Eduardo R. V.; Berndt, Jasper

    2016-03-01

    The importance of zircon in geochemical and geochronological studies, and its presence not only in aluminous but also in alkaline rocks, prompted us to think about a new zircon saturation model that can be applied in a wide range of compositions. Therefore, we performed zircon crystallization experiments in a range of compositions and at high temperatures, extending the original zircon saturation model proposed by Watson and Harrison (Earth Planet Sci Lett 64:295-304, 1983) and Boehnke et al. (Chem Geol 351:324-334, 2013). We used our new data and the data from previous studies in peraluminous melts, to describe the solubility of zircon in alkaline and aluminous melts. To this effect, we devised a new compositional parameter called G [ {( {3 \\cdot {{Al}}2 {{O}}3 + {{SiO}}2 )/({{Na}}2 {{O}} + {{K}}2 {{O}} + {{CaO}} + {{MgO}} + {{FeO}}} )} ] (molar proportions), which enables to describe the zircon saturation behaviour in a wide range of rock compositions. Furthermore, we propose a new zircon saturation model, which depends basically on temperature and melt composition, given by (with 1σ errors): ln [ {{Zr}} ] = ( {4.29 ± 0.34} ) - ( {1.35 ± 0.10} ) \\cdot ln G + ( {0.0056 ± 0.0002} ) \\cdot T( °C ) where [Zr] is the Zr concentration of the melt in µg/g, G is the new parameter representing melt composition and T is the temperature in degrees Celsius. The advantages of the new model are its straightforward use, with the G parameter being calculated directly from the molar proportions converted from electron microprobe measurements, the temperature calculated given in degrees Celsius and its applicability in a wider range of rocks compositions. Our results confirm the high zircon solubility in peralkaline rocks and its dependence on composition and temperature. Our new model may be applied in all intermediate to felsic melts from peraluminous to peralkaline compositions.

  11. Melt migration in a silicate liquid-olivine system - An experimental test of compaction theory

    NASA Technical Reports Server (NTRS)

    Riley, G. N., Jr.; Kohlstedt, D. L.; Richter, F. M.

    1990-01-01

    An experimentally derived melt migration profile is compared with those obtained from compaction theory. A couple is prepared in which a source-for-melt (a disk composed of a silicate glass and olivine) was placed in contact with a sink-for-melt (a disk of polycrystalline olivine) in order to induce melt migration under laboratory conditions. It is noted that melt infiltrates into the sink disk along triple junctions driven by capillary forces. In order to analyze the melt migration profile in terms of compaction theory, the equations developed by McKenzie (1984) to describe porous flow of a liquid in a deformable matrix were modified. The bouyancy force term is replaced with a capillary force term and governing equations are then solved numerically with the initial boundary conditions specified by the experimental design. Also, it is determined that compaction theory provides a good description of the experimental results provided that the permeability of these solid-liquid materials increases linearly with increasing liquid fraction.

  12. Silicate-natrocarbonatite liquid immiscibility in 1917 eruption combeite-wollastonite nephelinite, Oldoinyo Lengai Volcano, Tanzania: Melt inclusion study

    NASA Astrophysics Data System (ADS)

    Sharygin, Victor V.; Kamenetsky, Vadim S.; Zaitsev, Anatoly N.; Kamenetsky, Maya B.

    2012-11-01

    Primary silicate-melt and carbonate-salt inclusions occur in the phenocrysts (nepheline, fluorapatite, wollastonite, clinopyroxene) in the 1917 eruption combeite-wollastonite nephelinite at Oldoinyo Lengai. Silicate-melt inclusions in nepheline clearly show liquid immiscibility phenomena expressed in the presence of carbonate globules in silicate glass. The coexistence of inclusions with markedly different proportions of silicate glass + vapor-carbonate globule in the core of nepheline phenocrysts, the presence of carbonate-salt inclusions in fluorapatite and our heating experiments strongly suggest that their entrapment began at temperatures higher than 1130 °C in an intermediate chamber when initial carbonated nephelinite melt was heterogeneous and represented a mixture of immiscible liquids. Silicate-natrocarbonatite melt immiscibility took place at high temperature and immiscible nephelinite and carbonatite liquids coexisted over a wide temperature range from ≥ 1130 °C to 600 °C. Homogenization of a carbonate globule (dissolution of the gas bubble in carbonate melt) at 900-940 °C indicates that after separation from silicate magma the natrocarbonatite represented homogeneous liquid in the 900-1130 °C temperature range, whereas below these temperatures immiscible melts of different composition and fluid phase have separated from it. The bulk composition of homogeneous natrocarbonatite melt may be estimated as ≈ 20% CaF2, 40-60% (Na,K)2CO3 and 20-40% CaCO3 based on the coexistence of nyerereite, calcite and fluorite and the rapid phase transition (carbonate aggregate → carbonate liquid) at 550-570 °C observed in vapor-carbonate globules of nepheline-hosted silicate-melt inclusions and on the Na2CO3-CaCO3-CaF2 phase diagram. Silicate glasses of nepheline-hosted immiscible inclusions drastically differ from host nephelinite in the abundance of major and trace elements. They are high peralkaline ((Na + K)/Al — up to 9.5) and virtually free of water (H2

  13. Parameterized Lattice Strain Models for REE Partitioning between Amphibole and Silicate Melt

    NASA Astrophysics Data System (ADS)

    Shimizu, K.; Liang, Y.; Sun, C.; Jackson, C.; Saal, A. E.

    2015-12-01

    The distribution of REE between amphibole and silicate melt is important for understanding a variety of igneous processes involving amphibole. In general, amphibole-melt REE partition coefficients (DREE) depend on pressure (P), temperature (T), and compositions of amphibole and melt. A previous study parameterized the DREE in amphibole-melt solely as a function of melt composition [1]. Here, we use published REE partitioning data between amphibole and basaltic melt, the lattice strain model [2], and non-linear least squares regression method to parameterize key partitioning parameters in the lattice strain model (D0, r0, and E) as a function of P, T, and both amphibole and melt compositions. We focus on experimental data obtained by LA-ICP-MS and ion probe, and experiments close to equilibrium. Amphiboles and coexisting melts from the 38 experiments that we compiled span a wide range of compositions with the Mg# of amphibole and melt ranging from 36 to 100 and 15 to 99, respectively. Two models, which give nearly identical results, are explored in this study. In the first model, D0 is a function of T and amphibole composition: it negatively correlates with T and MgM1,2,3 content in amphibole, and positively correlates with TiM1,2,3 content in amphibole. In the second model, D0 is solely a function of the melt composition: it negatively correlates with the mole fraction of Ca in the melt. Interestingly, r0 and E are both constant and identical between the two models, suggesting D0 in the two models are equivalent. The latter allows us to develop a new thermometer for amphibole-melt equilibria. As an independent test, we compared model-derived temperatures with those reported in the phase equilibrium experiments. The predicted temperatures are within ±41°C on average of the reported temperatures, adding confidence to our parameterizations of D0. Our two parameterized lattice strain models can be used to model REE fractionation between amphibole and basaltic melts

  14. The effect of sulfide dissolved in silicate melts on enhancing the solubility of the Highly Siderophile Elements

    NASA Astrophysics Data System (ADS)

    O'Neill, H. S.

    2015-12-01

    There are large inconsistencies among experimental studies of Highly Siderophile Element (HSE) partitioning relations between silicates and metal or sulfide phases, which has usually been attributed to "micronuggets", a general term for sub-optical (approximately < 0.2 µm) particles or blobs of metal or sulfide in the silicate phase. But there have then been differences of opinion as to whether these micronuggets (and, sometimes, associated optical-sized metal or sulfide particles) should be viewed as contamination, or are produced by precipitation on quenching the experiment, which need to be included to recover true partitioning relations. Although quench precipitation is perhaps inevitable in experiments at extremely high temperatures and/or pressures, or with high loads of dissolved sulfide, it may be superimposed on the usual micronugget contamination. The problem is particularly acute in HSE sulfide-melt/silicate-melt partition coefficients, where results range over several orders of magnitude. Moreover, nearly all the reported results of directly determined sulfide-melt/silicate-melt partition coefficients are considerably lower than values calculated by combining metal/silicate-melt with metal/sulfide-melt partition coefficients. This discrepancy has been attributed to large effects of S dissolved as sulfide in the silicate melts on HSE solubilities. As such large effects are not expected from the thermodynamic modeling of sulfide solubilities in silicate melts, it has been proposed that HSEs dissolve in sulfide-containing silicate melts by forming HSE-S complexes. This idea has been tested by experiments that compare the solubilities of Ir, Re and Ru in a high-TiO2 silicate melt both with and without dissolved sulfide at 1400 to 1600ºC at atmospheric pressure. The high TiO2 suppresses micronuggets. Experiments were analysed by LA-ICP-MS, with detection limits approaching 2 ppb. For Ir, the results show that at fO2 low enough to enable measurable sulfide

  15. Melt migration in a silicate liquid-olivine system: An experimental test of compaction theory

    SciTech Connect

    Riley, G.N. Jr.; Kohlstedt, D.L. ); Richter, F.M. )

    1990-11-01

    To investigate the kinetics of porous flow in partially molten peridotite, a melt migration couple - formed from a disc of fine-grained olivine plus {approximately}15% of a synthetic K-Al silicate glass and a disc of polycrystalline olivine - was heated at 1,255C under a confining pressure of 300 MPa for 2 hr. Driven by capillary forces, silicate liquid in the source disc infiltrates along three-grain junctions into the sink disc. To analyze the resulting melt migration profile in terms of compaction theory, the equations developed by McKenzie (1984) to describe porous flow of a liquid in a deformable matrix were modified by replacing the buoyancy force term with a capillary force term. The governing equations were then solved numerically with the governing equations were then solved numerically with the initial and boundary conditions specified by the experimental design. Comparison of the melt migration profile obtained from the experiment with those generated by numerical simulation demonstrates that compaction theory provides a good description of the experimental results provided that the permeability of these solid-liquid materials increases linearly with increasing liquid fraction.

  16. High-temperature apparatus for chaotic mixing of natural silicate melts

    SciTech Connect

    Morgavi, D.; Petrelli, M.; Vetere, F. P.; González-García, D.; Perugini, D.

    2015-10-15

    A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10{sup 6} Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.

  17. High-temperature apparatus for chaotic mixing of natural silicate melts

    NASA Astrophysics Data System (ADS)

    Morgavi, D.; Petrelli, M.; Vetere, F. P.; Gonzalez, D.; Perugini, D.

    2015-12-01

    A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term ChaOtic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 106 Pas) natural silicate melts. The instrument represents an extraordinary advance because allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges in the volcanic environment. The COMMA device is tested at extreme conditions by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1170°C, with melts of shoshonitic and rhyolitic composition, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. We anticipate the COMMA to become a state-of-the-art apparatus for detailed investigations of magma mixing processes providing unprecedented information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.

  18. High-temperature apparatus for chaotic mixing of natural silicate melts

    NASA Astrophysics Data System (ADS)

    Morgavi, D.; Petrelli, M.; Vetere, F. P.; González-García, D.; Perugini, D.

    2015-10-01

    A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 106 Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.

  19. High-temperature apparatus for chaotic mixing of natural silicate melts.

    PubMed

    Morgavi, D; Petrelli, M; Vetere, F P; González-García, D; Perugini, D

    2015-10-01

    A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10(6) Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment. PMID:26520985

  20. A Microscopic View of Mass Transport in Silicate Melts by Quasielastic Neutron Scattering and Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Meyer, Andreas; Kargl, Florian; Horbach, Jürgen

    The application of quasielastic neutron scattering and molecular dynamics simulation to the study of mass transport in silicate melts is outlined. It is shown how the knowledge of atomic dynamics and structure reveals the mechanisms of mass transport. Peculiar properties of atomic diffusion and viscous flow behaviour as a function of melt composition are discussed in terms of the formation of alkali diffusion channels in the static structure. This non-homogeneous distribution of alkali ions in a disrupted tetrahedral Si-O network is investigated in binary lithium, sodium and potassium silicate melts and in ternary sodium aluminosilicates and sodium ironsilicates representing the main compositions of natural volcanic rocks.

  1. The formation of nuggets of highly siderophile elements in quenched silicate melts at high temperatures: Before or during the silicate quench?

    NASA Astrophysics Data System (ADS)

    Malavergne, V.; Charon, E.; Jones, J.; Cordier, P.; Righter, K.; Deldicque, D.; Hennet, L.

    2016-01-01

    The Highly Siderophile Elements (HSE) are powerful tracers of planetary differentiation. Despite the importance of their partitioning between silicate and metal for the understanding of planetary core formation, especially for the Earth and Mars, there is still a huge discrepancy between conclusions based on different high temperature (HT) experimental studies. These disagreements may be due to the presence of HSE micro and nanonuggets in HT experiments. The formation of these nuggets is still interpreted in different ways. One hypothesis is that these HSE nuggets formed during the quench of the silicate melt, while another hypothesis supposes that these nuggets formed before the quench and represented artefacts of HT experiments. The goal of this work is to clarify whether the presence of HSE nuggets in silicate melts is linked to a quench effect or not. Understanding the formation of these HSE nuggets represents thus a necessary step towards the resolution of the Earth's core formation scenarios. We performed new HT experiments (1275-2000 °C) at different oxygen fugacities (fO2), between ambient air up to ∼5 log units below the Iron-Wüstite buffer [IW-5], for two different silicate compositions (synthetic martian and terrestrial basalts) mixed with a metallic mixture of Pt-Au-Pd-Ru. Our 1275-1600 °C experiments were contained in either olivine, diopside or graphite crucible; experiments at 2000 °C were performed using a levitation method, so no capsule was necessary. Our samples contained quenched silicate melts, minerals (olivine, pyroxene, spinel depending on the run), a two-phase metallic bead and nano and micro-nuggets of HSE. Our samples underwent fine textural, structural and analytical characterizations. The distribution of the nuggets was not homogeneous throughout the quenched silicate melt. HSE nuggets were present within crystals. Dendritic textures from the quenched silicate melt formed around HSE nuggets, which could be crystallized, showing

  2. The influence of sulfur on platinum solubility in water-saturated silicate melts

    NASA Astrophysics Data System (ADS)

    Gorbachev, Pavel; Bezmen, Nikolay

    2010-05-01

    P.N. Gorbachev1 (IGEM RAS), N.I. Bezmen2 (IEM RAS), 1Institute of Ore Deposits, Petrography, Mineralogy and Geochemistry (I.G.E.M.), Russian Academy of Sciences; p_gor@mail.ru 2 Institute of Experimental Mineralogy Russian Academy of Sciences; bezmen@iem.ac.ru In order to assess the influence of sulfur on Pt solubility in silicate melts we studied the Pt solubility in S- and H2O-bearing silicate melt. Experimental conditions were the same that the previous studies with S-free silicate melts [1]. Platinum solubility was determined in silicate melt of Di55An35Ab10 composition at oxygen fugacities varying between the HM and IW buffer at 1200°C and fluid pressure from 2129 to 3211 kbars. Hydrogen mole fraction varied from 0.002 to 0.248; lg fO2 from -6.53 at MMO buffer to -11.86 at IW buffer. Experiments were conducted in a vertically orientated internally heated gas high pressure vessel under conditions of known gas speciation and controlled fugacities. Glass samples were polished before analysis to remove possible contamination by the metal of the capsule and then boiled for 1 h in concentrated HCl. The oxygen fugacity was controlled by the double capsule buffer technique in oxidizing conditions (NM-NNO buffers) and by an Ar-H2-gas mixture at reducing conditions (XH2 > 0.05). Durations of all experiments were 3 days. Platinum concentrations were determined by instrumental neutron activation analysis (INNA). A significant similarity on Pt solubility in the S-bearing and S-free melts was observed. At reducing conditions (log fO2 < NNO buffer) a systematic decrease of the Pt solubility with decreasing fO2 was observed (from 32.870 to 23.849 ppm for S-bearing and 76.200 to 20.610 ppm for S-free melts respectively). At oxidizing conditions with a higher S concentration in the melt an increase in Pt concentrations was observed (from 24.660 to 54.960 and from 23.400 to 54.781 respectively). The presence of sulfur has a insignificant effect on Pt solubility. Although our

  3. Partitioning of potassium between silicates and sulphide melts - Experiments relevant to the earth's core.

    NASA Technical Reports Server (NTRS)

    Goettel, K. A.

    1972-01-01

    The partitioning of potassium between roedderite, K2Mg5Si12O30 and an Fe-FeS melt was investigated at temperatures about 40 C above the Fe-FeS eutectic. Roedderite was considered a prime candidate for one of the potassium-bearing phases in the primitive earth because roedderite and merrihueite are the only two silicates containing essential potassium which have been identified in stony meteorites. Application of the results to a primitive chondritic earth is discussed, and it is concluded that extraction of most of the earth's potassium into the Fe-FeS core would occur under the conditions in the early earth.-

  4. Experimental Constraints on the Solubility and Partitioning of Carbon between Metallic and Silicate Melt in a Shallow Magma Ocean

    NASA Astrophysics Data System (ADS)

    Chi, Han

    The budget and origin of carbon in Earth and other terrestrial planets are debated and one of the key unknowns is the behavior and fate of carbon during early planetary processes including accretion, core formation, and magma ocean crystallization. Here we determine, experimentally, the solubility of carbon in coexisting Fe-Ni alloy melt and basaltic silicate melt in shallow magma ocean conditions, i.e., at 1-3 GPa, 1500-1800 °C. Oxygen fugacity of the experiments, estimated based on Fe (in metallic alloy melt)-FeO (in silicate melt) equilibrium, varied from IW-0.37 and IW-1.02, where IW refers to the oxygen fugacity imposed by the coexistence of iron and wustite. Four different starting mixes, each with 7:3 silicate:metal mass ratio, with silicate melt NBO/T (estimated proportion of non-bridging oxygen with respect to tetrahedral cations) ranging from 0.81 to 1.54 were studied. Concentrations of carbon in the alloy melt were determined using electron microprobe whereas carbon contents of quenched basaltic glasses were determined using secondary ionization mass spectrometry (SIMS). Identification of carbon and hydrogen-bearing species in silicate glasses was performed using Raman spectroscopy. Our results show that carbon in the metallic melt varies between 4.39 and 7.43 wt.% and increases with increasing temperature and modestly with increasing pressure. Carbon concentration in the silicate melts, on the other hand, varies from 11+/-1 ppm to 111+/-7 ppm and is negatively correlated with pressure but positively correlated with temperature, the NBO/T (non-bridging per tetrahydron, an index of the depolymerization of the silicate melt), the oxygen fugacity and the water content of the silicate melts. Raman and FT-IR results show that at our experimental conditions, carbon in silicate melt is dissolved as hydrogenated species, in addition to . The calculated carbon partition coefficient varies from 510+/-53 to 5369+/-217 and varies systematically as a function of P

  5. Investigating sulfur partitioning between nominally volatile-free minerals and silicate melts

    NASA Astrophysics Data System (ADS)

    Marzoli, A.; Callegaro, S.; Baker, D. R.; Geraki, K.; Maneta, V.

    2015-12-01

    Despite the key role played by volatile species in magmatic systems, it is still challenging to quantify their concentrations in ancient melts. We suggested a quantitative approach for estimating S contents in basaltic melts (Callegaro et al., 2014), based on direct measurement of S on clinopyroxene and calculation of its concentration in the melt through an experimentally determined partition coefficient (KD). We further investigated the partitioning of sulfur between silicate melts and nominally volatile-free minerals (olivine, orthopyroxene, clinopyroxene, and plagioclase), as well as between melt and amphibole. Partitioning experiments were performed with basaltic, andesitic and dacitic bulk compositions, at hydrous and anhydrous conditions, and at high and low oxygen fugacities (fO2), where sulfur in the melt is dominantly present as an S6+ or S2- species, respectively (Wilke et al., 2011). Sulfur concentrations in melts were measured by electron microprobe and in crystals by synchrotron X-ray fluorescence. At low fO2 the average crystal/liquid KDs for sulfur vary from 0.0004 (at a maximum) for olivine, to 0.003 (another maximum) for orthopyroxene, to 0.03 for clinopyroxene, and to 0.07 for plagioclase. The KDs correlate positively with the cation-oxygen bond lengths in the crystals. At high fO2 the KDs drop to approximately one-third of those observed at low fO2. These observations suggest that S2- replaces oxygen in the crystal structure. Water has no measureable influence on the crystal/melt partitioning of sulfur. Clinopyroxene/melt KDs are correlated with the Mg/(Mg+Fe) ratio of the crystal, but appear insensitive to the IVAl in the structure. Plagioclase/melt S partitioning appears unaffected by anorthite content and iron concentration in the crystal. These new KDs allow the determination of sulfur concentration in the igneous melts co-existing with these crystals and provide insights into the volatile concentrations of ancient magmas and their possible

  6. Partitioning of protactinium, uranium, thorium and other trace elements between columbite and hydrous silicate melt

    NASA Astrophysics Data System (ADS)

    Huang, F.; Schmidt, M. W.; Günther, D.; Eikenberg, J.

    2009-12-01

    U-series disequilibria are a unique powerful tool to constrain the time-scales and processes of magmatism in mid-ocean ridge, intra-plate, and convergent margin settings. 235U-231Pa is one of the important parent-daughter pairs (231Pa half life = 33 kyr) because protactinium is normally much more incompatible than U during magmatism and thus the ubiquitously observed 231Pa excess in young igneous rocks most likely reflects melting processes. However, because of the extreme incompatibility of protactinium in most silicate minerals (mineral/meltDPa < 10-5), it is quite challenging to experimentally investigate partition coefficient of Pa. Furthermore, it is unclear whether Pa is always +5 or possibly more reduced at natural magmatic conditions, in particular in a reduced mantle. This significantly limits our understanding of the chemical behavior of Pa and applications of U-series disequilibrium data to the study of magmatism. Columbite (Mn(Nb,Ta)2O6) is a mineral with Nb5+ and Ta5+ as major elements, and occurs in per-aluminous granites and pegmatites. Because protactinium is expected to be +5 charged at crustal oxygen fugacities, and Pa5+ has an ionic radius close to Nb5+ and Ta5+, Nb and Ta have been used as proxy elements to constrain partitioning of Pa between minerals and melt using lattice strain modeling. Nb and Ta are strongly compatible in columbite (columbite/meltDNb-Ta ~ 10), and lattice strain modeling based on physical characteristics of the Nb-Ta site where Pa should be incorporated predicts that columbite/meltDPa5+ should be around 0.2, high enough to be experimentally determined at the permissible Pa doping level of 10 ppm (bulk). Experiments were run in a piston cylinder apparatus at 0.5 GPa and 1115 oC using Pt double capsules with NNO or FMQ as external fO2 buffers. The starting material is a hydrous per-aluminous granitic composition, doped with Pa solution in the Paul Scherrer Institute and also contains other trace elements including U, Th, REE

  7. Io: Generation of Silicate Magma by Shear Melting at the Base of a Basaltic Lithosphere

    NASA Technical Reports Server (NTRS)

    Carr, M. H.

    1985-01-01

    Tidal theory and observational evidence indicates that about 1 w/sq. m. of energy is released at the surface of Io. In order to place limits on how much tidal energy can be dissipated within a rigid lithosphere, depth-temperature profiles were calculated for different lithosphere thickness assuming that the tidal energy was dissipated uniformly throughout the lithosphere. Thus a thick lithosphere implies that a significant fraction of the tidal energy is dissipated below the depth where solidus temperatures are reached. One possibility is that Io has a crust consisting of a low melting temperature fraction such as basalt, overlying a mantle of a high melting temperature fraction such as peridotite. Thus, if the lithosphere of Io is thicker than 30 km, as appears probable, then high rates of silicate volcanism are implied and a significant fraction of the tidal energy must be dissipated by viscous deformation rather than rigid flexure.

  8. The geochemical signature of fluid-saturated magma determined from silicate melt inclusions in ascension island granite xenoliths

    NASA Astrophysics Data System (ADS)

    Webster, J. D.; Rebbert, C. R.

    2001-01-01

    Silicate glasses in crystal-free to crystal-poor melt inclusions from two coarse-grained granite xenoliths in alkaline volcanic rocks of Ascension Island were analyzed for 29 major, minor, and trace elements. For most constituents, the glass compositions are similar to those of the volcanic whole rocks and the xenoliths; we interpret the glasses to be chemically representative of granite melt. The melt inclusions are silicic; alkaline; contain low S and P abundances; and are enriched in H 2O, Cl, F, and Na relative to K. Inclusions from one xenolith contain 1.3 wt.% F, on average, whereas those from the other xenolith contain half that amount. The melt inclusion compositions allow investigation of the means and extent of granite magma evolution. The presence of magmatic fluid inclusions in close proximity to melt inclusions in the phenocrysts indicates that the granite melt was saturated in one or more volatile phases (Roedder and Coombs, 1967). The Cl and H 2O contents of the melt inclusions are consistent with the exsolution of volatile phase(s) at pressures of 3000 to 2000 bars. The glasses also show trends involving the (Cl/H 2O) ratio and the incompatible trace elements in melt that are indicative of melt evolution via crystal fractionation of volatile phase-saturated melt. These trends should be useful for recognizing volatile phase saturation in other Cl-enriched melts.

  9. Viscosity of Carbonate-Silicate Melts Using Ultra-High Resolution Falling Sphere Viscometry

    NASA Astrophysics Data System (ADS)

    Hummer, D. R.; Kavner, A.; Manning, C. E.; Park, C.; Kono, Y.; Kenney-Benson, C.

    2014-12-01

    Carbonatites are carbon-rich magmas that participate in the deep-Earth carbon cycle, and may be precursors to many types of terrestrial magmatism. [1] Viscosity is a crucial parameter in determining migration rates and behavior of melts from the upper mantle to Earth's surface, but very little is known about the viscosity of carbonate-silicate liquids at conditions relevant to Earth's interior. To examine the viscosity of carbonate-silicate liquids as a function of composition, we performed in situ falling sphere viscosity experiments using a high speed X-ray camera and Paris-Edinburgh press at the HPCAT beamline (Advanced Photon Source, Argonne National Laboratory). Mixtures from the CaCO3-CaSiO3 (calcite-wollastonite) binary system were used to simulate mantle silicate carbonatites. Samples were loaded using the experimental setup of Yamada et al [2], held at 3 GPa, and heated until the sample was fully molten (between 1350-1650 oC). The high speed camera recorded the falling rate of a platinum sphere placed near the top of the sample chamber, enabling the calculation of terminal velocity and hence viscosity. Results indicate that pure CaCO3 at upper mantle conditions has a very low viscosity of ~0.006 Pa-s, only a little higher than that of water. This viscosity is 2-6 times lower than that of potassium carbonates at similar pressures (2.5-4.0 GPa) but at somewhat lower temperatures (800-1200 oC). [3] Our measured viscosity as a function of increasing silicate content increases along a log-linear trend, reaching 0.256 Pa-s for CaSiO3 liquid. This heavy dependence of viscosity on composition has implications for melt migration processes at different depths, suggesting either viscosity-driven or porosity-driven migration depending on both extent of melting and carbonate content. [1] Dasgupta, R. et al. (2013) Nature 493, 211-215. [2] Yamada, A. et al. (2011) Rev. Sci. Instr. 82, 015103. [3] Dobson, D. et al. (1996) Earth Plan. Sci. Lett. 143, 207-215.

  10. Spin crossover and iron-rich silicate melt in the Earth's deep mantle (Invited)

    NASA Astrophysics Data System (ADS)

    Hirose, K.; Nomura, R.; Ozawa, H.; Tateno, S.; Hernlund, J. W.

    2010-12-01

    The volume difference between a silicate solid and its melt diminishes at high pressure, and the possibility that a melt sufficiently enriched in iron might then become more dense than solids at the pressures in the interior of the Earth and other terrestrial bodies has long been a source of considerable speculation. The occurrence of such dense silicate melts in the Earth's lowermost mantle would carry important consequences for its physical and chemical evolution and could provide a unifying model for explaining a variety of observed features in the core-mantle boundary (CMB) region [e.g., Labrosse et al., 2007 Nature]. Recent theoretical calculations [Stixrude et al., 2009 EPSL] combined with estimates of Fe partitioning between (Mg,Fe)SiO3 perovskite and melt at shallower mantle conditions suggest that melt is more dense than solids at pressures in the Earth's deepest mantle, consistent with analysis of shockwave experiments. Here we extend measurements of Fe partitioning in (Mg0.89Fe0.11)2 SiO4 bulk composition over the entire mantle pressure range, by a combination of laser-heated diamond-anvil cell experiments and chemical analyses of recovered samples using field-emission-type electron microprobe (FE-EPMA). The results demonstrate that the Fe-Mg distribution coefficient KD = ([FePv]/[MgPv]) / ([Femelt]/[Mgmelt]) between perovskite and melt is about 0.25 up to 75 GPa, consistent with earlier data found at 25 GPa in Al-free or -depleted peridotite materials using multi-anvil apparatus. On the other hand, the KD suddenly dropped to 0.07±0.02 at 76 GPa, resulting in strong Fe-enrichment in melts. It was almost constant at 0.06-0.08 at higher pressures to 159 GPa. The value did not change practically across the perovskite to post-perovskite phase transition. Additional x-ray emission spectroscopy measurements on (Mg0.95Fe0.05)SiO3 glass indicate the loss of spin around 60-70 GPa, suggesting that the observed change in Fe partitioning could be explained by a

  11. Properties of Silicate Melts at High Pressure and Temperature from Ab Initio Calculations

    NASA Astrophysics Data System (ADS)

    Seclaman, A. C.; Caracas, R.

    2014-12-01

    The evolution of planetary interiors is intrinsically connected to the behavior and properties of silicate melts at high pressures and temperatures. Our work comes as a complement to existing data expanding the pressure, temperature, and compositional ranges. We used the V.A.S.P. code to perform NVT Molecular Dynamics simulations on two basic compositions: Mg2SiO4 and MgSiO3. All calculations are done within augmented planar wave formalism of the Density Functional Theory. Supercells of 160 atoms clino-enstatite and 112 atoms forsterite were melted at 5000K and then cooled and thermalized, using the Nose-Hoover thermostat, at temperatures more representative of Earth's interior (3000 and 4000K). The pressure range of our investigations spans from 0 to approximately 160GPa. Since important properties, density and magnetism, are dependent on the presence of iron we also created (Fex-1,Mgx)SiO3 and (Fex-1,Mgx)2SiO4melts from the thermalized pure compositions by replacing the desired amount of magnesium atoms with iron. Because other transitional elements present similar behavior as iron, and nickel is an important element in the core, compositions containing different amounts of nickel were also created by adding extra Ni atoms in the system. We analyze in detail the behavior with pressure of the density, clustering and coordination, total magnetization, and thermodynamical parameters of the melts. Our results indicate that changes in the structure and magnetic moment of the Forsterite melt begin at relatively low pressure. As an application of our data to the Earth's present deep interior we analyzed in great detail various possible mixtures of Fe bearing melt and solid mantle in an attempt to fit the density estimated for the Ultra Low Velocity Zones.

  12. VOLATILECALC: A silicate melt-H2O-CO2 solution model written in Visual Basic for excel

    USGS Publications Warehouse

    Newman, S.; Lowenstern, J. B.

    2002-01-01

    We present solution models for the rhyolite-H2O-CO2 and basalt-H2O-CO2 systems at magmatic temperatures and pressures below ~ 5000 bar. The models are coded as macros written in Visual Basic for Applications, for use within MicrosoftR Excel (Office'98 and 2000). The series of macros, entitled VOLATILECALC, can calculate the following: (1) Saturation pressures for silicate melt of known dissolved H2O and CO2 concentrations and the corresponding equilibrium vapor composition; (2) open- and closed-system degassing paths (melt and vapor composition) for depressurizing rhyolitic and basaltic melts; (3) isobaric solubility curves for rhyolitic and basaltic melts; (4) isoplethic solubility curves (constant vapor composition) for rhyolitic and basaltic melts; (5) polybaric solubility curves for the two end members and (6) end member fugacities of H2O and CO2 vapors at magmatic temperatures. The basalt-H2O-CO2 macros in VOLATILECALC are capable of calculating melt-vapor solubility over a range of silicate-melt compositions by using the relationships provided by Dixon (American Mineralogist 82 (1997) 368). The output agrees well with the published solution models and experimental data for silicate melt-vapor systems for pressures below 5000 bar. ?? 2002 Elsevier Science Ltd. All rights reserved.

  13. Prediction of plagioclase-melt equilibria in anhydrous silicate melts at 1-atm

    NASA Astrophysics Data System (ADS)

    Namur, Olivier; Charlier, Bernard; Toplis, Michael J.; Vander Auwera, Jacqueline

    2012-01-01

    Many models for plagioclase-melt equilibria have been proposed over the past 30 years, but the focus is increasingly on the effects of water content and pressure. However, many geological and petrological applications concern low pressure and low water systems, such as the differentiation of large terrestrial basaltic magma chambers, and lunar and asteroidal magmatism. There is, therefore, a justified need to quantify the influence of anhydrous liquid composition on the composition of equilibrium plagioclase at 1-atm. With this in mind, a database of over 500 experimentally determined plagioclase-liquid pairs has been created. The selected low pressure, anhydrous, experiments include both natural and synthetic liquids, whose compositions range from basalt to rhyolite. Four equations are proposed, derived from this data. The first is based on a thermodynamically inspired formalism, explicitly integrating the effect of temperature. This equation uses free energies and activities of crystalline anorthite available from the literature. For the activity of anorthite in the liquid phase, it is found that current models of the activity of individual oxides are insufficient to account for the experimental results. We have therefore derived an empirical expression for the variation of anorthite activity in the liquid as a function of melt composition, based upon inversion of the experimental data. Using this expression allows the calculation of plagioclase composition with a relative error less than 10%. However, in light of the fact that temperature is not necessarily known for many petrological applications, an alternative set of T-independent equations is also proposed. For this entirely empirical approach, the database has been divided into three compositional groups, treated independently for regression purposes: mafic-ultramafic, alkali-rich mafic-ultramafic, and intermediate-felsic. This separation into distinct subgroups was found to be necessary to maintain errors

  14. Silicate melt inclusions in clinopyroxene phenocrysts from mafic dikes in the eastern North China Craton: Constraints on melt evolution

    NASA Astrophysics Data System (ADS)

    Cai, Ya-Chun; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Liu, Xuan; Liu, Yongsheng

    2015-01-01

    Silicate melt inclusions (SMIs) in magmatic minerals provide key information on the chemical and mineralogical evolution of source magmas. The widespread Cretaceous mafic dikes in the Jiaojia region of the eastern North China Craton contain abundant SMIs within clinopyroxene phenocrysts. The daughter minerals in these SMIs include amphibole, plagioclase, pyrite and ilmenite, together with CO2 + CH4 and CH4 as the major volatile phase. The total homogenization temperatures of the SMIs range between 1280 and 1300 °C. The host clinopyroxene phenocrysts in these dolerite dikes are dominantly augite with minor diopside. From LA-ICPMS analyses of the SMIs, we identify two compositional groups: (1) low-MgO (6.0-7.6 wt.%) SMIs and (2) high-MgO (11.2-13.9 wt.%) SMIs. The Low-MgO group exhibits higher concentrations of TiO2, Al2O3, Na2O, P2O5 and lower CaO and CaO/Al2O3 ratio as compared to the high-MgO SMIs. The trace element patterns of the two types of SMIs are similar to those of the host mafic dikes. However, the low-MgO SMIs and host mafic dikes are clearly more enriched in all the trace elements as compared to the high-MgO type, especially with regard to the highly incompatible elements. The estimated capture temperatures and pressures are 1351-1400 °C and 1.6-2.1 GPa for the high-MgO SMIs and 1177-1215 °C and 0.6-1.1GPa for the low-MgO type. The high-MgO and low-MgO SMIs were trapped at depths of ∼51-68 km and ∼20-35 km, respectively. Computations show that the parental melt is mafic with SiO2 content 49.6 wt% and Mg# 80.0 with relatively low total alkali contents (1.35 wt% Na2O + K2O) and high CaO (15.2 wt%). Exploratory runs with the program MELTS and pMELTS show that the low-MgO and high-MgO SMIs were derived from the same parental melt through different degrees of crystallization. Clinopyroxene and a small amount of olivine were the fractionating phases during the evolution from parental melts to high MgO melts, while the low MgO melts experienced

  15. Reaction rim growth on olivine in silicic melts: Implications for magma mixing

    USGS Publications Warehouse

    Coombs, M.L.; Gardner, J.E.

    2004-01-01

    Finely crystalline amphibole or pyroxene rims that form during reaction between silicic host melt and cognate olivine xenocrysts, newly introduced during magma mixing events, can provide information about the timing between mixing and volcanic eruptions. We investigated rim growth experimentally by placing forsteritic olivine in rhyolitic and rhyodacitic melts for times between 25 and 622 h at 50 and 150 MPa, H2O-saturated, at the Ni-NiO buffer. Rims of orthopyroxene microlites formed from high-silica rhyolite and rhyodacite melts at 885??C and 50 MPa, and in the rhyolite at 150 MPa and 885??C. Rims of amphibole with lesser orthopyroxene formed in the rhyolite at 150 MPa and 800??C and in the rhyodacite at 150 MPa and 885??C. Irregular, convolute olivine edges and mass balance between olivine, melt, and rim phases show that olivine partly dissolved at all conditions. Iron-rich zones at the exteriors of olivines, which increased in width parabolically with time, show that Fe-Mg interdiffusion occurring in olivines was not outpaced by olivine dissolution. Linear increases of the square of rim widths with time suggest that diffusion within the melt is the rate-controlling process for olivine dissolution and rim growth. Rims grew one-half to one order-of-magnitude faster when melt water contents were doubled, unless conditions were far above the liquidus. Rim growth rate in rhyolite increases from 0.055 ?? 0.01 ??m2/h at 885 ??C and 50 MPa to 0.64 ?? 0.13 ??m2/h at 800 ??C and 150 MPa. Melt composition has a lesser effect on rim growth rates, with growth rate increasing as melt SiO2 content decreases. Pyroxene rims on olivines in andesite erupted from Arenal volcano (Costa Rica) grew at a rate of 3.0 ?? 0.2 ??m2/h over an eleven-year period. This rate is faster than those of the experiments due to lower melt viscosity and higher temperatures, and suggests that a magma mixing event preceded the start of the eruption by days.

  16. Solubility of Au in Intermediate Silicate Melts : Experimental Demonstration of the Effect of S

    NASA Astrophysics Data System (ADS)

    Jego, S.; Pichavant, M.; Mavrogenes, J.

    2006-05-01

    Copper-gold-molybdenum deposits represent major metal resources known to be spatially and temporally associated with intrusive arc magmatism (Hedenquist and Lowenstern, 1994). Although the bulk of the ore metals seem to originate from the magmas, there is as yet no consensus on processes responsible for their concentration. The fact that primary ore minerals are predominantly sulfides has led to the suggestion that sulfur may play an important role in metal enrichment processes at the magmatic stage (Sillitoe, 1997; Mungall, 2002). Previous experimental studies have shown that sulfides can largely fractionate gold from the melt, and therefore concluded that oxidized magmas are more likely to be Au-enriched. Here, we conducted high- pressure temperature experiments (4 Kbar, 1000°C) on three natural dacitic magmas from the Philippines (two adakites and one typical calc-alkaline composition) over a range of fO2 corresponding to reducing (~NNO-1), moderately oxidizing (~NNO+1.5) and strongly oxidizing (~NNO+3) conditions as measured by solid Ni-Pd-O sensors. The experiments were carried out in gold capsules, the latter also serving as the source of gold, in the presence of variable amounts of H2O. The water content of experimental glasses was determined by Karl-Fisher Titration. Both S-free and S-bearing (~1 wt% S added) experiments were performed. Sulfur concentrations in experimental glasses were measured by electron microprobe, and an empirical model was used to compute the fS2 of the experimental charges. Gold concentrations in glasses were determined by LA-ICP-MS. Charges consist of dominant silicate melt quenched to glass plus minor silicate phases (mostly Cpx, rarely Opx). All S-bearing charges are saturated with either sulfides or sulfates, together with discrete Au-Fe-S alloys, depending on the fO2. Our data show that gold solubility in S-free charges is low (50-100 ppb, depending on the melt composition) but increases with fO2 in a way consistent with AuO0

  17. Partitioning of Mo, P and other siderophile elements (Cu, Ga, Sn, Ni, Co, Cr, Mn, V, and W) between metal and silicate melt as a function of temperature and silicate melt composition

    NASA Astrophysics Data System (ADS)

    Righter, K.; Pando, K. M.; Danielson, L.; Lee, Cin-Ty

    2010-03-01

    Metal-silicate partition coefficients can provide information about the earliest differentiation histories of terrestrial planets and asteroids. Systematic studies of the effects of key parameters such as temperature and melt composition are lacking for many elements. In particular, data for Mo is scarce, but given its refractory nature, is of great value in interpreting metal-silicate equilibrium. Two series of experiments have been carried out to study Mo and P partitioning between Fe metallic liquid and basaltic to peridotitic silicate melt, at 1 GPa and temperatures between 1500 and 1900 °C. Because the silicate melt utilized was natural basalt, there are also measurable quantities of 9 other siderophile elements (Ni, Co, W, Sn, Cu, Mn, V, Cr, Ga and Zn). The Ni and Co data can be used to assess consistency with previous studies. In addition, the new data also allow a first systematic look at the temperature dependence of Cu, Ga, Sn, Cr, Mn V and W for basaltic to peridotitic melts. Many elements exhibit an increase in siderophile behavior at higher temperature, contrary to popular belief, but consistent with predictions from thermodynamics. Using these new data we examine DMomet/sil and DPmet/sil in detail and show that increasing temperature causes a decrease in the former and an increase in the latter, whereas both increase with MgO content of the silicate melt. The depletions of Mo and P in the mantle of the Earth can be explained by metal-silicate equilibrium at magma ocean conditions — both elements are satisfied at PT conditions of an intermediate depth magma ocean for the Earth 22.5 GPa and 2400 °C.

  18. A Model For Multicomponent Fluid Saturation In C-o-h-s-silicate Melt Systems

    NASA Astrophysics Data System (ADS)

    Moretti, R.; Papale, P.; Ottonello, G.

    The dissolution behavior of volatile components in magmas is essential to model the volcanic process from the deep regions of magma generation and storage to the shal- low regions of magma eruption and emplacement. Water, carbon dioxide, and sulfur compounds are the main volatile components in nat- ural magmas, constituting in most cases more than 99% of the volcanic gases released before, during, and after eruption. We have developed a method to calculate the chem- ical equilibrium between a fluid phase in the C-O-H-S system and a silicate melt with composition defined by ten major oxides. The method is based on a previous model for the saturation of H2O-CO2 fluids [1] and on a sulfur solubility model [2] in silicate liquids. For the computation of the fugacities of components in fluids with complex composition we used the SUPERFLUID code [3]. The model allows determining the partition of H2O, CO2, and S between the silicate liquid and the coexisting fluid, and the composition of the fluid phase in terms of H2O, CO2, SO2, and H2S, as a func- tion of pressure, temperature, volatile-free liquid composition, oxygen fugacity, and total amount of each volatile component in the system. App lications are presented to several silicate liquids with rhyolitic and basaltic composition, oxygen fugacities in the range NNO +/- 2, and pressure from a few hundred MPa to atmospheric, with the simplifying assumption that no reduced or oxidized sulfur-saturated solid or liquid phases nucleate or separate from the liquid-gas system. Results show the well-known minima in sulfur saturation contents as a function of oxygen fugacity, the reciprocal effects of volatiles on their saturation contents, and the complex relationships between saturation surface of a multicomponent fluid, liquid composition, volatile abundance, P-T conditions, and oxidation state. The method represents therefore a new powerful tool for the prediction of multicomponent gas-melt equilibria in magmas. REFERENCES [1

  19. Insights into Silicate and Oxide Melt Structure from Amorphous, Non-Glass-Forming Materials

    NASA Astrophysics Data System (ADS)

    Stebbins, J. F.

    2015-12-01

    Many silicate and oxide liquids of interest in the Earth sciences and in technology cannot readily be quenched to glasses, either because of low silica contents (and hence low viscosity at the melting point and accompanying liquid 'fragility') or because of liquid-liquid unmixing at high temperature. Although in-situ, high temperature structural tools have been in use for decades and are rapidly developing, many methods are still most informative for glass samples quenched to ambient pressure and temperature, e.g. high-resolution solid-state NMR. Amorphous oxides, including alumina and silicate compositions, have widespread technological applications. These are generally deposited by a variety of high-energy sputtering methods, as films of thicknesses of 10's to 100's of nm. Using Al-27, Si-29, and O-17 NMR, we have recently shown that for such films, very similar short-range structure is seen in materials made by very different kinetic pathways, such as sol-gel synthesis vs. ion-beam sputtering. This path-independent structure suggests that these materials pass through transient equilibrium states during their formation, probably that of deeply supercooled liquids just above glass transition temperatures. In the HfO2-SiO2 and ZrO2-SiO2 systems, for example, samples have well-resolved O-17 NMR spectra, allowing quantitation of O sites with only Hf(Zr) neighbors (so-called "free" oxide ions), with mixed Hf(Zr) and Si neighbors, and Si only. The observed oxygen speciation agrees well with a simple thermodynamic model of one of the most fundamental equilibria in silicate systems, namely the reaction of bridging (Si-O-Si) and "free" (e.g. OHf3 and OHf4) oxide ions to produce "non-bridging" oxygens (e.g. Si-OHf2). This new approach to sampling such structural equilibria in compositions far outside the range of normal glass-forming liquids may provide new insights into more geological compositions as well, as well as in more general models of silicate melt chemistry.

  20. Occurrence of silicate melt, carbonate-rich melt and fluid during medium pressure anatexis of metapelitic gneisses (Oberpfalz, Bavaria) revealed by melt and fluid inclusions study

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; O'Brien, Patrick; Hecht, Lutz; Wunder, Bernd

    2014-05-01

    of a silicate melt and a carbonate-rich melt during anatexis at relatively shallow crustal levels, but this hypothesis needs to be further tested through re-homogenization experiments by piston cylinder means. References Bartoli, O., Cesare, B., Poli, S., Bodnar, R.J., Acosta-Vigil, A., Frezzotti, M.L. & Meli, S., 2013. Recovering the composition of melt and the fluid regime at the onset of crustal anatexis and S-type granite formation. Geology, 41, 115-118. Cesare, B., Ferrero, S., Salvioli-Mariani, E., Pedron, D. & Cavallo, A., 2009. Nanogranite and glassy inclusions: the anatectic melt in migmatites and granulites. Geology, 37, 627-630. Ferrero, S., Bartoli, O., Cesare, B., Salvioli Mariani, E., Acosta-Vigil, A., Cavallo, A., Groppo, C. & Battiston, S., 2012. Microstructures of melt inclusions in anatectic metasedimentary rocks. Journal of Metamorphic Geology, 30, 303-322. Ferrero, S., Braga, R., Berkesi, M., Cesare, B. & Laridhi Ouazaa, N., 2014. Production of Metaluminous melt during fluid-present anatexis: an example from the Maghrebian basement, La Galite Archipelago, central Mediterranean. Journal of Metamorphic Geology, DOI:10.1111/jmg.12068. Tanner, D.C. & Behrmann, J.H., 1995. The Variscan tectonics of the Moldanubian gneisses, Oberpfalzer Wald: a compressional history. Neues Jahrbuch fur Geologie und Palaontologie. Abhandlungen, 197, 331-355. Touret, J.L.R., 2009. Mantle to lower-crust fluid/melt transfer through granulite metamorphism. Russian Geology and Geophysics, 50, 1052-1062.

  1. Microscopic origins of macroscopic properties of silicate melts and glasses at ambient and high pressure: Implications for melt generation and dynamics

    NASA Astrophysics Data System (ADS)

    Lee, Sung Keun

    2005-07-01

    Recent development and advances in solid state NMR, together with theoretical analyses using quantum-chemical calculations and statistical mechanical modeling, have allowed us to estimate and quantify the detailed distributions of cations and anions in model silicate glasses and melts with varying pressure, temperature and composition. How these microscopic, atomic-scale distributions in the melts from NMR and simulations affect the thermodynamic and transport properties relevant to magmatic processes has been extensively explored recently. Here, based on these previous studies, we present a classification scheme to quantify the various aspects of disorder in covalent oxide glasses and melts on scales of less than 1 nm. The scheme includes contributions from both chemical and topological disorder. Chemical disorder can further be divided into [1] connectivity, which quantifies the extent of mixing among framework units (often parameterized by the degree of Al avoidance or phase separation) and the extent of polymerization (mixing between framework and nonframework cations), and [2] nonframework disorder, which denotes the distribution of network-modifying or charge-balancing cations. Topological disorder includes the distribution of bond lengths and angles. We use this framework of disorder quantification to summarize recent progress on the structures of silicate melts and glasses, mainly obtained from 2D triple quantum magic-angle spinning (3QMAS) NMR, as functions of temperature, pressure, and composition. Most glasses and melts studied show a tendency for chemical ordering in connectivity, nonframework disorder and topological disorder at ambient and high pressure. The chemical ordering in framework disorder, a manifestation of energetics in the melts and glasses, contributes to the total negative deviation of activity of oxides from ideal solution in silicate melts (reduced activity). While no definite evidence of clustering among nonframework cations was found

  2. Aubrite basalt vitrophyres: High sulfur silicate melts and a snapshot of aubrite formation. [Abstract only

    NASA Technical Reports Server (NTRS)

    Fogel, R. A.

    1994-01-01

    Two aubrite basalt vitrophyre clasts have been found within AMNH thin sections from the Parsa EH3 chondrite and the Khor Temiki aubrite. Polished sections of the Parsa Aubrite Inclusion (PAI) and the Khor Temiki Inclusion (KTI) were studied by optical, electron probe microanalysis (EPMA), and scanning electron microscopy (SEM) techniques with broad-beam and low absorbed EPMA currents used to minimize glass volatile loss. Some data have previously been reported for PAI and KTI may possibly correlate to a previously reported inclusion in Khor Tiimiki. In polished sections, PAI and KTI are approximately equal 4 mm in diameter and contain a large volume of glass. The clasts have similar textural characteristics and are akin to lunar vitrophyre textures. The glasses have high alkali rhyodacitic compositions Al-though PAI is peraluminous, KTI is significantly peralkaline. Additionally, the glasses have elevated sulfur concentrations that are extremely high by geochemical standards. SEM examination for beam overlap of microscopic CaS, FeS, and (Mg, Mn, Fe) S inclusions showed no such contamination. Furthermore, homogeneity of glass S content and low FeO contents help rule out contamination. Materials research data show that under reducing conditions alumino-silicate melts can dissolve up to several weight percent sulfur in the absence of Fe. The high S and alkali contents, the lack of associated high shock features, and the rationalized phase equilibria suggest that PAI and KTI are igneous melting products of an E-chondrite-like source material. Although large-scale impact melting cannot totally be ruled out, the above observations eliminate the possibility of in-situ shock melting.

  3. Hydroclast and Peperite generation: Experimental Results produced using the Silicate Melt Injection Laboratory Experiment

    NASA Astrophysics Data System (ADS)

    Downey, W. S.; Mastin, L. G.; Spieler, O.; Kunzmann, T.; Shaw, C. S.; Dingwell, D. B.

    2008-12-01

    The Silicate Melt Injection Laboratory Experiment (SMILE) allows for the effusive and explosive injection of molten glass into a variety of media - air, water, water spray, and wet sediments. Experiments have been preformed using the SMILE apparatus to evaluate the mechanisms of "turbulent shedding" during shallow submarine volcanic eruptions and magma/wet-sediment interactions. In these experiments, approximately 0.5 kg of basaltic melt with 5 wt.% Spectromelt (dilithium tetraborate) is produced in an internally heated autoclave at 1150° C and ambient pressure. The molten charge is ejected via the bursting of a rupture disc at 3.5 MPa into the reaction media, situated within the low pressure tank (atmospheric conditions). Preliminary experiments ejecting melt into a standing water column have yielded hydroclasts of basalt. SEM images of the clasts show ubiquitous discontinuous skins ("rinds") that are flaked, peeled, or smeared away in strips. Adhering to the clast surfaces are flakes, blocks, and blobs of detached material, up to 10 μm in size. The presence of partially detached rinds and rind debris likely reflects repeated bending, scraping, impact, and other disruption through turbulent velocity fluctuations. These textures are comparable to littoral explosive deposits at Kilauea Volcano, Hawaii, where lava tubes are torn apart by wave action, the lava is quenched, and thrown back on the beach as loose fragments (hyaloclastite). Preliminary experiments injecting melt into wet sediments show evidence of sediment ingestion and fluidal textures. These results support the interpretation that peperite generation can be driven by hydrodynamic mixing of a fuel and a coolant.

  4. An Occurrence of H2 in Silicate Melt Inclusions in Quartz from Granite of Jiajika Granitic Pegmatite Deposit, China

    NASA Astrophysics Data System (ADS)

    Li, J.; Chou, I.-M.

    2014-06-01

    Laser Raman spectroscopic analyses of silicate melt inclusions in quartz, from granite of Jiajika Li-bearing pegmatite deposit in China, revealed the existence of H_2 in the vapor phase with unknown mechanisms for the formation and retention of H_2.

  5. In-situ thermal emissivity of silicate melts: an example from Erebus phonolitic volcano

    NASA Astrophysics Data System (ADS)

    Hao, Li; Joan, Andújar; Sousa Meneses Domingos, De; Bruno, Scaillet; Patrick, Echegut

    2014-05-01

    Real time thermal remote sensing of active volcanic systems is a crucial technique for understanding the behavior and eruptive activity of hot magmatic bodies. By determining the temperature of an erupting magma, researchers can have a better understanding on the rheology of active lava flows and domes, and have a first approach to the composition, flow pattern and cooling rate of the melt. Such measurements rely on determining the thermal infrared emissivity of the magma, a parameter that is crucial for understanding the heat transfer and radiative cooling of the system. Nevertheless, previous works have shown that the thermal emissivity of a silicate melt is strongly affected by changes in the composition, melt structure, presence of crystals or existence of a glassy crust. Hence, small changes on these parameters will have an important impact on retrieved temperatures (i.e., Lee et al. 2013). Within this context we have performed in-situ thermal emission spectroscopy measurements on two different samples: 1) a natural phonolitic glass/melt from Erebus and 2) an haplo-phonolitic synthetic glass/melt. We used a direct method to obtain a spectrum in the wavenumber range from 400 to 13000 cm-1; the samples were heated up from room temperature to 1600K with a CO2 laser and data were collected during all the heating stage with a FTIR spectrometer. The first results show that both samples have a different emissivity response while being heated up. Whereas the synthetic sample shows no-variation in emissivity while heated, the natural Erebus glass sample, however, experienced a sudden jump in emissivity (from 0.7 to 0.95) beyond 2000 cm-1 near the glass-transition temperature. After this point, emissivity decreases with increasing temperature (to 0.8). We have also explored the thermal behavior of the natural phonolite during cooling. A low cooling rate increases sample emissivity to values that are similar to those at the glass transition (from 0.8 to 0.95) but beyond

  6. Recalescence in Silicate Melts: More Than Just a Flash in the Pan?

    NASA Astrophysics Data System (ADS)

    Whittington, A. G.; Sehlke, A.

    2015-12-01

    Rapid cooling of silicate melts facilitates undercooling, where nucleation is delayed and crystal growth begins at temperatures below equilibrium. In such cases, rapid crystal growth and release of latent heat of crystallization can produce net heating (recalescence). We have documented recalescence in Fe-Mg pyroxene and komatiite melts, using a thermal imaging (FLIR) camera for melt volumes on the order of cm3, and using differential scanning calorimetry for melt volumes on the order of mm3. On cooling Fe0.8Mg1.2Si2O6 liquid from ~1600˚C in air, at ~30˚C/s, crystallization begins at ~1110˚C. Averaging over the whole base of the crucible (~10cm2), the observed temperature increase is ~100˚C and it takes ~2.5 seconds to attain the thermal peak. Crystallization and heating can be seen migrating across the melt volume together. When looking at a 3x3 pixel spot (~1mm2 in our setup), reheating to >1270˚C occurred in ~1 s. About 30 mg of the same melt was cooled in a differential scanning calorimeter. Cooled at ~1˚C/s, two distinct crystallization peaks were seen at ~1450 and ~1270˚C. Cooled at ~2˚C/s, the first peak was delayed to ~1315˚C and merged with the second. Examination of recovered samples indicates crystallization of enstatite, followed by Fe-oxides and tridymite in a silica-rich glass matrix. On cooling of komatiite liquid from ~1600˚C at ~50˚C/s, crystallization begins at ~1080˚C. The average temperature plateaus for ~2s and then continues cooling. When looking at a 3x3 pixel spot, heating of ~10˚C could be detected only by comparing different video frames. We conclude that (i) thermal imaging of lava flows needs to be conducted with mm-scale spatial resolution to assess true temperature fluctuations, and (ii) thermal models that incorporate latent heat of crystallization as an "effective heat capacity" term do not allow recalescence, and may inaccurately capture the thermal history of rapidly cooled lava.

  7. Breakdown of orthopyroxene contributing to melt pockets in mantle peridotite xenoliths from the Western Qinling, central China: constraints from in situ LA-ICP-MS mineral analyses

    NASA Astrophysics Data System (ADS)

    Su, Ben-Xun; Zhang, Hong-Fu; Yang, Yue-Heng; Sakyi, Patrick Asamoah; Ying, Ji-Feng; Tang, Yan-Jie

    2012-03-01

    Major and trace element compositions of constituent minerals, partly decomposed rims of orthopyroxenes (DRO), `closed' melt pockets (CMP) and open melt pockets (OMP) in some Western Qinling peridotite xenoliths were obtained by LA-ICP-MS. Systematic core-to-rim compositional variations of garnet, clinopyroxene and orthopyroxene demonstrate that these minerals underwent variable degrees of subsolidus breakdown or partial melting. Both DROs and CMPs consist of similar mineral assemblages and are characterized by high TiO2, CaO + Na2O and low MgO contents; they are enriched in LREE and LILE compositions, have positive anomalies in Pb, Sr and particularly Ti, negative Th and U, and variable Zr and Hf anomalies. These chemical features are distinct and reflect reactions involving the orthopyroxenes. Compared to the CMPs, the OMPs, which are composed of a complex assemblage of minerals, display lower FeO and MgO contents, larger ranges in SiO2 and Na2O, higher TiO2, Al2O3, CaO and trace element concentrations, slightly negative Zr and Hf anomalies, and apparently negative Ti anomalies. Modeling calculations of partial fusion of orthopyroxenes and clinopyroxenes suggest that the CMPs most likely originated from the breakdown of orthopyroxenes with variably minor contribution of external melts from the melting of clinopyroxenes, whereas the OMPs were probably formed from the modification of the CMPs through the interaction with large amount of external melts.

  8. Crystallization of diamond from a silicate melt of kimberlite composition in high-pressure and high-temperature experiments

    SciTech Connect

    Arima, Makoto; Nakayama, Kazuhiro ); Akaishi, Minoru; Yamaoka, Shinobu; Kanda, Hisao )

    1993-11-01

    In high-pressure and high-temperature experiments (1800-2200[degrees]C and 7.0-7.7 GPa), diamond crystallized and grew in a volatile-rich silicate melt of kimberlite composition. This diamond has well-developed [111] faces, and its morphologic characteristics resemble those of natural diamond but differ from those of synthetic diamond grown from metallic solvent-catalysts. The kimberlite melt has a strong solvent-catalytic effect on diamond formation, supporting the view that some natural diamonds crystallized from volatile-rich melts in the upper mantle. 19 refs., 3 figs., 1 tab.

  9. The solubility of carbon monoxide in silicate melts at high pressures and its effect on silicate phase relations. [in terrestrial and other planetary interiors

    NASA Technical Reports Server (NTRS)

    Eggler, D. H.; Mysen, B. O.; Hoering, T. C.; Holloway, J. R.

    1979-01-01

    Autoradiographic analysis and gas chromatography were used to measure the solubility in silicate melts of CO-CO2 vapors (30 to 40% CO by thermodynamic calculation) in equilibrium with graphite at temperatures up to 1700 deg C and pressures to 30 kbar. At near-liquidus temperatures CO-CO2 vapors were found to be slightly more soluble than CO2 alone. As a result of the apparently negative temperature dependence of CO solubility, the solubility of CO-CO2 at superliquidus temperatures is less than that of CO2. Melting points of two silicates were depressed more by CO than by CO2. Phase boundary orientations suggest that CO/CO + CO2 is greater in the liquid than in the vapor. The effect of the presence of CO on periodotite phase relations was investigated, and it was found that melts containing both CO and CO2 are nearly as polymerized as those containing only CO2. These results suggest that crystallization processes in planetary interiors can be expected to be about the same, whether the melts contain CO2 alone or CO2 and CO.

  10. Partitioning of H2O between olivine and carbonate-silicate melts at 6.3 GPa and 1400 °C: Implications for kimberlite formation

    NASA Astrophysics Data System (ADS)

    Sokol, Alexander G.; Kupriyanov, Igor N.; Palyanov, Yuri N.

    2013-12-01

    Partitioning of H2O between olivine and carbonate-silicate melts has been studied at 6.3 GPa and 1400 °C using a split-sphere multianvil apparatus. Olivine was synthesized in equilibrium with hydrous silicate and hydrous carbonate-silicate±chloride melts saturated with respect to one of Opx, Grt, Ms or a harzburgitic (Ol+Opx+Grt) residue and had CO2/(CO2+SiO2) molar ratios from 0 to 0.8. The concentration of H2O in olivine was determined using FTIR spectroscopy. We found that depending on the melt carbonation and saturation in equilibrium silicate phases the H2O content in olivine varied from 100 to 1500 ppm. The obtained results and data reported in Sokol et al. (2013) indicate that H2O content in olivine becomes approximately two times lower as CO2/(CO2+SiO2) molar ratios in the equilibrium melt increases from 0 to 0.4-0.8 and the crystallization media transform from hydrous silicate to hydrous carbonate-silicate (kimberlite like) melt. The estimated water partitioning between carbonate-silicate melt and nominally anhydrous mantle minerals indicates that carbonatitic melt can effectively extract water once it invades H2O-poore the peridotite. We suggest that extraction of H2O owing to the freezing point depression may provide the necessary melting degree of metasomatized peridotite source and formation of kimberlitic magma.

  11. Melt fracturing and healing: A mechanism for degassing and origin of silicic obsidian

    USGS Publications Warehouse

    Cabrera, A.; Weinberg, R.F.; Wright, H.M.N.; Zlotnik, S.; Cas, Ray A.F.

    2011-01-01

    We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 ??C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian. ?? 2011 Geological Society of America.

  12. Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

    NASA Astrophysics Data System (ADS)

    Namur, Olivier; Charlier, Bernard; Holtz, Francois; Cartier, Camille; McCammon, Catherine

    2016-08-01

    Chemical data from the MESSENGER spacecraft revealed that surface rocks on Mercury are unusually enriched in sulfur compared to samples from other terrestrial planets. In order to understand the speciation and distribution of sulfur on Mercury, we performed high temperature (1200-1750 °C), low- to high-pressure (1 bar to 4 GPa) experiments on compositions representative of Mercurian lavas and on the silicate composition of an enstatite chondrite. We equilibrated silicate melts with sulfide and metallic melts under highly reducing conditions (IW-1.5 to IW-9.4; IW = iron-wüstite oxygen fugacity buffer). Under these oxygen fugacity conditions, sulfur dissolves in the silicate melt as S2- and forms complexes with Fe2+, Mg2+ and Ca2+. The sulfur concentration in silicate melts at sulfide saturation (SCSS) increases with increasing reducing conditions (from <1 wt.% S at IW-2 to >10 wt.% S at IW-8) and with increasing temperature. Metallic melts have a low sulfur content which decreases from 3 wt.% at IW-2 to 0 wt.% at IW-9. We developed an empirical parameterization to predict SCSS in Mercurian magmas as a function of oxygen fugacity (fO2), temperature, pressure and silicate melt composition. SCSS being not strictly a redox reaction, our expression is fully valid for magmatic systems containing a metal phase. Using physical constraints of the Mercurian mantle and magmas as well as our experimental results, we suggest that basalts on Mercury were free of sulfide globules when they erupted. The high sulfur contents revealed by MESSENGER result from the high sulfur solubility in silicate melt at reducing conditions. We make the realistic assumption that the oxygen fugacity of mantle rocks was set during equilibration of the magma ocean with the core and/or that the mantle contains a minor metal phase and combine our parameterization of SCSS with chemical data from MESSENGER to constrain the oxygen fugacity of Mercury's interior to IW- 5.4 ± 0.4. We also calculate that

  13. Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS

    NASA Astrophysics Data System (ADS)

    Gualda, G. A.; Ghiorso, M. S.; Begue, F.; Pamukcu, A. S.; Gravley, D. M.

    2013-12-01

    been formed from two laterally-juxtaposed magma reservoirs. (2) For the Peach Spring Tuff (SW USA), we find that most matrix glass compositions yield no pressure estimates; only compositions with highest Na2O (>3.5 wt. %) and lowest K2O (<5.5 wt. %) can be in simultaneous equilibrium with quartz and 2 feldspars, which is expected from pumice mineralogy. This suggests that the rhyolite-MELTS barometer can be used to filter out compositions compromised by alteration or analytical problems. Inferred crystallization pressures are in the range 190-260 MPa. (3) For the Mamaku-Ohakuri paired eruption (Taupo Volcanic Zone, New Zealand), we find that only glass inclusion and matrix glass compositions with SiO2 >78.4 wt. % yield pressure estimates; for higher SiO2, the melt is too silicic to be in simultaneous equilibrium with both quartz and plagioclase. Inferred crystallization pressures are <130 MPa, consistent with relatively shallow magma storage in the Taupo Volcanic Zone. Glass inclusions yield higher pressures than matrix glass, suggesting that matrix glass records crystallization during eruptive decompression.

  14. Carbon dioxide and argon diffusion in silicate melts: Insights into the CO 2 speciation in magmas

    NASA Astrophysics Data System (ADS)

    Spickenbom, K.; Sierralta, M.; Nowak, M.

    2010-11-01

    To investigate the influence of temperature and composition on the diffusivities of dissolved carbon dioxide and argon in silicate melts, diffusion experiments were performed at magmatic pressure and temperature conditions in (a) albite melts with excess Na 2O (0-8.6 wt%) and a constant Si/Al ratio of 3, and (b) albite 70quartz 30 to jadeite melts with decreasing SiO 2 content and a constant Na/Al ratio of 1. We obtained diffusion coefficients at 500 MPa and 1323-1673 K. In the fully polymerized system Ab 70Qz 30 - Jd, the change in composition only has a weak effect on bulk CO 2 diffusivity, but Ar diffusivity increases clearly with decreasing SiO 2 content. In the system Ab + Na 2O, bulk CO 2 and Ar diffusivity increase significantly with gradual depolymerisation. The relatively small change in composition on molar basis in the depolymerized system leads to a significantly larger change in diffusivities compared to the fully polymerized Ab 70Qz 30-Jd join. Within error, activation energies for bulk CO 2 and Ar diffusion in both systems are identical with decreasing silica content (Ab + Na 2O: 159 ± 25 kJ mol -1 for bulk CO 2 and 130 ± 8 kJ mol -1 for Ar; Ab 70Qz 30-Jd: 163 ± 16 kJ mol -1 for bulk CO 2 and 148 ± 15 kJ mol -1 for Ar) even though this results in depolymerisation in one system and not the other. Although there is a variation in CO 2 speciation with changing composition as observed in quenched glasses, it has previously established that this is not a true representation of the species present in the melt, with the ratio of molecular CO 2 to carbonate decreasing during quenching. Thus, diffusion coefficients for the individual CO 2 species cannot be directly derived by measuring molecular CO 2 and CO 32- concentration-distance profiles in the glasses. To obtain diffusivities of individual CO 2 species, we have made two assumptions that (1) inert Ar can be used as a proxy for molecular CO 2 diffusion characteristics as shown by our previous work and

  15. Partitioning of Moderately Siderophile Elements Among Olivine, Silicate Melt, and Sulfide Melt: Constraints on Core Formation in the Earth and Mars

    NASA Technical Reports Server (NTRS)

    Gaetani, Glenn A.; Grove, Timothy L.

    1997-01-01

    This study investigates the effects of Variations in the fugacities of oxygen and sulfur on the partitioning of first series transition metals (V, Cr, Mn, Fe, Co, Ni. and Cu) and W among coexisting sulfide melt, silicate melt, and olivine. Experiments were performed at 1 atm pressure, 1350 C, with the fugacities of oxygen and sulfur controlled by mixing CO2, CO, and SO2 gases. Starting compositions consisted of a CaO-MgO-Al2O3-SiO2-FeO-Na2O analog for a barred olivine chondrule from an ordinary chondrite and a synthetic komatiite. The f(sub O2)/f(sub S2), conditions ranged from log of f(sub O2) = -7.9 to - 10.6, with log of f(sub S2) values ranging from - 1.0 to -2.5. Our experimental results demonstrate that the f(sub O2)/f(sub S2) dependencies of sulfide melt/silicate melt partition coefficients for the first series transition metals arc proportional to their valence states. The f(sub O2)/f(sub S2) dependencies for the partitioning of Fe, Co, Ni, and Cu are weaker than predicted on the basis of their valence states. Variations in conditions have no significant effect on olivine/melt partitioning other than those resulting from f(sub O2)-induced changes in the valence state of a given element. The strong f(sub O2)/f(sub S2) dependence for the olivine/silicate melt partitioning of V is attributable to a change of valence state, from 4+ to 3+, with decreasing f(sub O2). Our experimentally determined partition coefficients are used to develop models for the segregation of sulfide and metal from the silicate portion of the early Earth and the Shergottite parent body (Mars). We find that the influence of S is not sufficient to explain the overabundance of siderophile and chalcophile elements that remained in the mantle of the Earth following core formation. Important constraints on core formation in Mars are provided by our experimental determination of the partitioning of Cu between silicate and sulfide melts. When combined with existing estimates for siderophile

  16. In situ insights to Se (S) partitioning between silicate and metallic melts at extreme conditions

    NASA Astrophysics Data System (ADS)

    Borchert, M.; Petitgirard, S.; Appel, K.; Watenphul, A.; Morgenroth, W.

    2012-12-01

    The Earth's core mainly consists of a metallic Fe-Ni mixture. However, seismic observations show that the density is about 5-10% lower than expected for an Fe-Ni alloy under similar pressure and temperature conditions (e.g., [1,2]). This discovery initiated numerous studies to identify and quantify light elements in the Earth0s core. Among others, sulphur has been suggested to be a promisingly candidate to alloy with the metallic core because of its depletion in the crust and the mantle relative to other volatile elements by several orders of magnitude (e.g., [3-5]). In the last decades, several experimental studies have aimed to quantify the sulphur content in the Earth's core and to determine its influence on the physical properties (e.g., [6]). However, experimental data on sulphur partitioning between silicate and metallic liquids at pressures and temperatures relevant for core-mantle boundary conditions are missing. This lack is due to pressure and temperature limitations of conventional experimental approaches (up to 25 GPa and 2200 K). New developments, like laser-heated diamond-anvil cells (LDAC), allow studies at core-mantle boundary conditions, but in-situ chemical analysis of sulphur in LDACs is impossible due to the high absorption of S fluorescence in the diamonds. Instead of sulphur, selenium can be used to model sulphur partitioning between silicate and metallic melts at elevated PT conditions. This is based on the fact that sulphur and selenium can be considered as geochemical twins ([7,8]). The main advantage of this approach is the much higher excitation energy of selenium compared to sulphur, which enables in-situ XRF analysis in LDACs. Here, we present preliminary data on Se partitioning between silicate and metallic melt at extreme conditions. The experiments have been performed in double-sided laser-heated LDACs at the high pressure beamlines P02.2 (DESY, Germany) and ID27 (ESRF, France) as described in [9]. Micro-XRF mappings are used to

  17. Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

    NASA Astrophysics Data System (ADS)

    Namur, Olivier; Charlier, Bernard; Holtz, Francois; Cartier, Camille; McCammon, Catherine

    2016-04-01

    Chemical data from the MESSENGER spacecraft revealed that surface rocks on Mercury are unusually enriched in sulfur compared to samples from other terrestrial planets. In order to understand the speciation and distribution of sulfur on Mercury, we performed high temperature (1200-1750°C), low- to high-pressure (1 bar to 4 GPa) experiments on compositions representative of Mercurian lavas and on the silicate composition of an enstatite chondrite. We equilibrated silicate melts with sulfide and metallic melts under highly reducing conditions (IW-1.5 to IW-9.4; IW = iron-wüstite oxygen fugacity buffer). Under these oxygen fugacity conditions, sulfur dissolves in the silicate melt as S2‑ and forms complexes with Fe2+, Mg2+ and Ca2+. The sulfur concentration in silicate melts at sulfide saturation (SCSS) increases significantly with increasing reducing conditions (from < 1 wt.% S at IW-2 to >10 wt.% S at IW-8) and with increasing temperature. At sulfide saturation, the composition of the sulfide melt is mainly composed of FeS at IW-2 to IW-6 whereas it also contains (Mg,Ca,Fe)S under more reducing conditions (< IW-6). Metallic melts have a low sulfur content which decreases from 3 wt.% at IW-2 to 0 wt.% at IW-9. Based on our new data and those from previous studies, we developed a parameterization to predict SCSS in Mercurian magmas as a function of melt composition, temperature, pressure and oxygen fugacity. Using physical constraints of the Mercurian mantle and magmas as well as our experimental results, we suggest that basalts on Mercury were free of sulfide globules when they erupted. The high sulfur contents revealed by MESSENGER result from the high sulfur solubility in silicate melt at reducing conditions. By combining our parameterization of SCSS with chemical data from MESSENGER, we constrain the oxygen fugacity of Mercury's interior to IW-5.4±0.4 when the lavas were produced in the mantle. We also estimate that the mantle of Mercury most probably contains

  18. Resolving Histories of Magmatic Volatiles in Fluids and Silicate Melts as a Function of Pressure, Temperature, and Melt Composition through Apatite Geochemistry

    NASA Astrophysics Data System (ADS)

    Webster, J. D.; Piccoli, P. M.; Goldoff, B. A.

    2012-12-01

    Fluids including aqueous or aqueous-carbonic vapor, aqueous liquid, and hydrosaline liquid, if present in magma, influence magmatic and volcanic processes, and the exsolution of fluids from magma sequesters and buffers volatile components from melt thus impacting the textural and chemical evolution of melts and phenocrysts. Establishing the timing of initial magmatic fluid saturation and monitoring changes in fluid chemistry through textural interpretations are often challenging because primary magmatic fluid inclusions are uncommon to most plutonic systems and are extremely rare in phenocrysts of eruptive magmas. Moreover, miarolitic cavities, often interpreted to be a priori evidence of fluid exsolution, are rarely observed in igneous systems. Geochemical tools used to resolve magmatic volatile histories include the analysis and interpretation of melt inclusion compositions and those of hydrous minerals including micas, amphiboles, and apatite. We have conducted more than 50 new hydrothermal experiments involving apatite+rhyodacite melt±fluids at 28, 50, 100, 200, and 400 MPa, and have combined these new data with published results for apatite-saturated melts at 200 MPa. This integrated body of data supports determination of a broadly applicable geochemical relationship that correlates the mole fractions of H2O and Cl in apatite with mole fractions of H2O and Cl in coexisting silicate melt as a function of pressure, temperature, and melt composition (for felsic to basaltic melts). The mathematical expression of this relationship is useful for a wide variety of applications: constraining H2O, Cl, and F concentrations in silicate melts and hence verifying concentrations of magmatic volatiles determined from silicate melt inclusions; establishing pressures or temperatures of apatite crystallization or last equilibration with melt ± fluids (if temperature and pressure, respectively, are constrained from other geothermobarometers); determining concentrations of

  19. Temperature and pressure dependence of Ni partitioning between olivine and high-MgO silicate melts

    NASA Astrophysics Data System (ADS)

    Matzen, A. K.; Baker, M. B.; Beckett, J.; Stolper, E. M.

    2010-12-01

    Mantle melting that produces ocean island basalts (OIBs) takes place at temperatures (T) and pressures (P) significantly higher than the conditions at which they erupt or are intruded in the crust/shallow upper mantle [1]. To the degree that the olivine (ol)-liquid (liq) nickel partition coefficient depends on T and P, it is important that models used to describe ol-liq Ni partitioning during mantle melting include data from experiments at elevated T and P. The expressions can then be used in models which aim to reproduce the wide range of Ni contents measured in primitive phenocrysts from OIBs [2]. Available data on Ni partitioning is dominated by 1-atm experiments in which T and liquid composition are highly correlated, making it difficult to separate the effects of these variables on the observed variations in Ni partitioning between ol and liq based on 1-atm experiments alone [3].
    We conducted experiments on a mixture of MORB and olivine at 1 atm (1400°C) and 1-3 GPa (1450-1550°C). We moderated the loss of Ni from the silicate melt to the Pt-enclosed graphite capsule by surrounding the chip of MORB glass with powdered olivine and sintering the assembly at a T below the solidus of the MORB chip. The data presented in this work is from a series of reversed experiments where T and P were increased in such a way that the liquid composition remained approximately constant (MgO ~ 17 wt. %), effectively isolating the effects of T and P from those of liquid composition on the ol-liq partition coefficient. The resulting partition coefficient decreases from ~5 to 3.8 (by wt) as the temperature increases from 1400 to 1550°C. The rate of decrease of the Ni partition coefficient measured in these experiments (~0.5/100°C) is less than that of recent models, which predict a decrease of ~0.1/100°C [4]. Using the results of our experiments we fit a thermodynamic expression to describe the ol-liq Ni-Mg exchange equilibrium as a function of both T and liquid

  20. Partitioning of potassium between silicates and sulphide melts: Experiements relevant to the earth's core

    NASA Technical Reports Server (NTRS)

    Goettel, K. A.

    1972-01-01

    The partitioning of potassium between roedderite, K2Mg5Si12O30 and an Fe-FeS melt was investigaged at temperatures about 40 C above the Fe-FeS eutectic. Roedderite was considered a prime candidate for one of the potassium-bearing phases in the primitive earth because roedderite and merrihueite are the only two silicates containing essential potassium which have been identified in stony meteorites. A mean K2S/FeS weight ratio of (3.340 + or - 0.015) x 0.001 was determined in these experiments; a K2S/FeS weight ratio of about 0.01 would be sufficient to extract all potassium in a chondritic earth into the core. Application of these results to a primitive chondritic earth is discussed and it is concluded that extraction of most of the earth's potassium into the Fe-FeS core would occur under the conditions in the early earth.

  1. Viscosity and chemical diffusion of halogens in silicate melts: implications for volcanic degassing

    NASA Astrophysics Data System (ADS)

    Wasik, A.; Dingwell, D. B.; Courtial, P.; Hess, K.

    2005-12-01

    The efficiency of degassing processes in subduction zone volcanism may be affected by the magmato-hydrothermal geochemistry of halogens. In addition halogens may act as potential monitors of degassing efficiency and provide answers to the question of the role of disequilibrium during partitioning. Too little is known quantitatively about the transport properties of halogens in silicate melts. In particular, an accurate study of the transport properties of halogens should help to unlock the information contained in halogen concentrations of eruptive products and volcanic gases. For these reasons the chemical diffusivities of the halogens (fluorine, bromine, chlorine and iodine) have been measured in the synthetic Fe-bearing sodium disilicate melts, within a wide range of temperature (650-1400° C). The experiments were performed using diffusion couple technique. Halogens were added to the starting material in the form of FeF3, FeBr3, FeCl3 and FeI2 and stirred in concentric cylinder viscometer. The temperature was restricted to 1000-1100° C to avoid volatilization of halogens. After synthesis the samples were drilled, cut into 2mm disks and then doubly polished. Prepared disks were putted into platinum tubes (5mm diameter) and sealed by welding. The halogen rich sample was located at the bottom. During the experiments the temperature was monitored with a thermocouple located at the vicinity of the capsule. Run durations were between 30 minutes and 1 hour. The recovered samples were analyzed using an electron microprobe in order to determine the diffusion profiles of the halogens. The results were obtained by using Boltzmann-Matano method and they suggest at least 3 orders of magnitude range at 1000° C between the diffusion coefficients for F, Br, Cl and I. The fastest diffusing species was found to be fluorine, the slowest - iodine. In order to place the diffusivity measurements in the context of their extrinsic versus intrinsic nature, viscosity measurements were

  2. Volatile-rich silicate melts from Oldoinyo Lengai volcano (Tanzania): Implications for carbonatite genesis and eruptive behavior

    NASA Astrophysics Data System (ADS)

    de Moor, J. Maarten; Fischer, Tobias P.; King, Penelope L.; Botcharnikov, Roman E.; Hervig, Richard L.; Hilton, David R.; Barry, Peter H.; Mangasini, Frederick; Ramirez, Carlos

    2013-01-01

    This study presents volatile, trace, and major element compositions of silicate glasses (nepheline-hosted melt inclusions and matrix glass) from the 2007-2008 explosive eruption at Oldoinyo Lengai volcano, Tanzania. The bulk compositions of the heterogeneous ash erupted in 2007-2008 are consistent with physical mixing between juvenile nephelinite magma and natrocarbonatite emplaced during the preceding ˜25 years of effusive carbonatite eruption. The melt inclusions and matrix glasses span a wide range of silica-undersaturated compositions, from ˜46 wt% SiO2 and (Na+K)/Al˜3 in the least evolved melt inclusions to 38 wt% SiO2 and (Na+K)/Al up to 12 in the matrix glass. The depletion in SiO2 between melt inclusions and matrix glass is accompanied by strong enrichment in all of the incompatible trace elements measured (Ba, Nb, La, Ce, Sr, Zr, Y), which is consistent with fractional crystallization of a bulk mineral assemblage with SiO2 higher than that of the melt inclusions but inconsistent with silicate melt evolution by assimilation of carbonatite. The melt inclusions are volatile-rich with 2.7 wt% to 8.7 wt% CO2 and 0.7 wt% to 10.1 wt% H2O, indicating that Oldoinyo Lengai is a hydrous system. This is contrary to the long-held assumption that Oldoinyo Lengai is relatively anhydrous, which is based on the observation that natrocarbonatite lavas are water-poor. We argue that natrocarbonatites are derived from hydrous carbonate liquid that degas H2O at low pressure. The silicate glass data show that H2O concentration is negatively correlated with incompatible element enrichment, which we attribute to crystallization of the melt in response to decompression degassing of H2O. The eruptive cycle at Oldoinyo Lengai reflects changes in bulk silicate magma viscosity due to extensive H2O-driven crystallization and explosive eruptions occur when volatiles (i.e. H2O>CO2 gas, and carbonate liquid) cannot separate from the crystal-rich nephelinite magma. Melt H2O content

  3. The Effect of fO2 on Partition Coefficients of U and Th between Garnet and Silicate Melt

    NASA Astrophysics Data System (ADS)

    Huang, F.; He, Z.; Schmidt, M. W.; Li, Q.

    2014-12-01

    Garnet is one of the most important minerals controlling partitioning of U and Th in the upper mantle. U is redox sensitive, while Th is tetra-valent at redox conditions of the silicate Earth. U-series disequilibria have provided a unique tool to constrain the time-scales and processes of magmatism at convergent margins. Variation of garnet/meltDU/Th with fO2 is critical to understand U-series disequilibria in arc lavas. However, there is still no systematic experimental study about the effect of fO2 on partitioning of U and Th between garnet and melt. Here we present experiments on partitioning of U, Th, Zr, Hf, Nb, Ta, and REE between garnet and silicate melts at various fO2. The starting material was hydrous haplo-basalt. The piston cylinder experiments were performed with Pt double capsules with C-CO, MnO-Mn3O4 (MM), and hematite-magnetite (HM) buffers at 3 GPa and 1185-1230 oC. The experiments produced garnets with diameters > 50μm and quenched melt. Major elements were measured by EMPA at ETH Zurich. Trace elements were determined using LA-ICP-MS at Northwestern University (Xi'an, China) and SIMS (Cameca1280 at the Institute of Geology and Geophysics, Beijing, China), producing consistent partition coefficient data for U and Th. With fO2 increasing from CCO to MM and HM, garnet/meltDU decreases from 0.041 to 0.005, while garnet/meltDTh ranges from 0.003 to 0.007 without correlation with fO2. Notably, garnet/meltDTh/U increases from 0.136 at CCO to 0.41 at HM. Our results indicate that U is still more compatible than Th in garnet even at the highest fO2 considered for the subarc mantle wedge (~NNO). Therefore, we predict that if garnet is the dominant phase controlling U-Th partitioning during melting of the mantle wedge, melts would still have 230Th excess over 238U. This explains why most young continental arc lavas have 230Th excess. If clinopyroxene is the dominant residual phase during mantle melting, U could be more incompatible than Th at high fO2

  4. Kinetics of iron redox reaction in silicate melts: A high temperature Xanes study on an alkali basalt

    NASA Astrophysics Data System (ADS)

    Cochain, B.; Neuville, D. R.; de Ligny, D.; Roux, J.; Baudelet, F.; Strukelj, E.; Richet, P.

    2009-11-01

    In Earth and Materials sciences, iron is the most important transition element. Glass and melt properties are strongly affected by iron content and redox state with the consequence that some properties (i.e. viscosity, heat capacity, crystallization...) depend not only on the amounts of Fe2+ and Fe3+, but also on the coordination state of these ions. In this work we investigate iron redox reactions through XANES experiments at the K-edge of iron. Using a high-temperature heating device, pre-edge of XANES spectra exhibits definite advantages to make in-situ measurements and to determine the evolution of redox state with time, temperature and composition of synthetic silicate melts. In this study, new kinetics measurements are presented for a basalt melt from the 31,000-BC eruption of the Puy de Lemptegy Volcano in France. These measurements have been made between 773 K and at superliquidus temperatures up to 1923 K.

  5. Partitioning of Ni between olivine and siliceous eclogite partial melt: experimental constraints on the mantle source of Hawaiian basalts

    NASA Astrophysics Data System (ADS)

    Wang, Zhengrong; Gaetani, Glenn A.

    2008-05-01

    Olivine is abundant in Earth’s upper mantle and ubiquitous in basaltic lavas, but rarely occurs in eclogite. Partial melts of eclogite are, therefore, not in equilibrium with olivine, and will react with peridotite as they migrate through the upper mantle. If such melts erupt at Earth’s surface, their compositions will be highly modified and they may be olivine-saturated. We investigated experimentally the reaction between olivine and siliceous eclogite partial melt, and determined element partitioning between olivine and the melt produced by this reaction. Our results demonstrate that mixing of reacted eclogite partial melt with primitive basalt is capable of producing the positive correlation between melt SiO2 content and olivine Ni content observed in some Hawaiian lavas. Experiments were carried out by equilibrating eclogite partial melt or basalt with San Carlos olivine at 1 bar and 1,201 1,350°C. Our results show that eclogite partial melts equilibrated with mantle olivine retain their high SiO2, low FeO and MgO characteristics. Further, olivine-melt partition coefficients for Ni measured in these experiments are significantly larger than for basalt. Mixing of these melts with primitive Hawaiian tholeiitic lavas results in crystallization of high-Ni olivines similar to those in Makapuu-stage Koolau lavas, even though the mixed magmas have only moderate Ni contents. This results from a hyperbolic increase of the Ni partition coefficient with increasing polymerization of the mixed melt. Note that while eclogite partial melt in contact with peridotite will equilibrate with pyroxene as well as olivine, this will have the effect of buffering the activity of SiO2 in the reacted melt at a higher level. Therefore, an eclogite partial melt equilibrated with harzburgite will have higher SiO2 than one equilibrated with dunite, enhancing the effects observed in our experiments. Our results demonstrate that an olivine-free “hybrid” pyroxenite source is not

  6. Reactions between molten iron and silicate melts at high pressure: Implications for the chemical evolution of Earth's core

    NASA Astrophysics Data System (ADS)

    Ito, E.; Morooka, K.; Ujike, O.; Katsura, T.

    1995-04-01

    Reactions between molten iron and silicate melt were investigated with mixtures of pure iron and silicates (1Fe + 3MgSiO3 enstatite and 1Fe(+) 3(Mg(sub 0.9)Fe(sub 0.1)2SiO4 olivine in volumetric ratio) as starting materials at pressures of 10-26 GPa and temperatures of about 2500 C. The results show that a certain amount of Si (up to about 2%) dissolves in molten iron from silicate melt and that the dissolution is enhanced with increasing pressure. Many small spherical blobs composed of SiO2 and FeO present in coalesced iron grains were interpreted as quenched immiscible liquid formed during cooling. Therefore O also dissolves in molten iron under the experimental conditions. No evidence for dissolution of Mg was obtained. The present study also indicates that Si and O are important light elements of Earth's core if core segregation occurred in the deep magma ocean. The chemical evolution of Earth's core is discussed on the bases of the current core formation model and the present experimental results.

  7. Compressibility of hydrated and anhydrous sodium silicate-based liquids and glasses, as analogues for natural silicate melts, by Brillouin scattering spectroscopy

    NASA Astrophysics Data System (ADS)

    Tkachev, Sergey Nikolayevich

    A mathematical formalism was tested on compressibility studies of water, before applying it to the high pressure-temperature compressibility studies of hydrated and anhydrous sodium silicate-based liquids and glasses. The hypersonic sound velocity, refractive index and attenuation coefficient obtained using Brillouin light scattering spectroscopy technique were in agreement with literature data. From the measured sound velocities, the pressure dependence of the bulk moduli and density of liquid water were calculated, using Vinet equation of state. The formalism was extended to the Brillouin scattering studies of the elastic properties of alkaline-calcium silica hydrogels and float glass, which exhibits a dramatic increase in the pressure dependence of longitudinal velocity and a discontinuity in the compressibility at about 6 GPa. It is demonstrated that an apparent second-order transition to a new amorphous phase can form via the abrupt onset of a new compressional mechanism, which may be triggered by a shift in polymerization of the glass or an onset of a change in coordination of silicon. Brillouin scattering measurements were carried out on an aqueous solution of Na2O-2SiO2 and anhydrous Na2O-2SiO 2 glass and liquid at high P-T conditions. The "modified" platelet scattering geometry has allowed a determination of the longitudinal velocity independently from refractive index, and hence the adiabatic compressibility and density of liquids as a function of pressure and temperature. The observed increase in density of the melt and glass phases formed at high P-T conditions is likely associated with structural effects. The large values of KS' of the liquid phase illustrate that the means of compaction of the liquid differs substantially from that of the glass, and that the liquid is able to access a wider range of compaction mechanisms. The measured bulk modulus of Na2O-2SiO2 aqueous solution is closer to values of silicate melts than to that of end-member water at

  8. Storage Conditions of Large Silicic Magmatic Systems: Gauging Melt Evolution from Melt Inclusions Hosted in Different Phenocryst Phases

    NASA Astrophysics Data System (ADS)

    Grocke, S. B.; de Silva, S. L.; Wallace, P. J.; Kent, A. J.; Hervig, R. L.; Andrews, B. J.; Cottrell, E.

    2014-12-01

    Quartz- and sanidine-hosted melt inclusions from the 3.49 Ma rhyolitic Tara pumice fall deposit erupted from the Guacha II Caldera in SW Bolivia provide new insights into the melt evolution preceding a supereruption. Melt inclusions were analyzed for volatile contents using two different techniques, Fourier Transform Infrared Spectroscopy (FTIR) and ion microprobe (SIMS). Data from FTIR on quartz-hosted melt inclusions reveal pre-eruptive CO2 concentrations (maximum ~ 300 ppm), and H2O contents (average = 4.3 wt.%) that are similar to H2O contents derived from SIMS on the same inclusions (average = 4.2 wt.%). Melt inclusions in sanidine yield higher CO2 concentrations (maximum ~ 400 ppm) than those hosted in quartz, yet yield much lower H2O contents (average = 2.5 wt.% via FTIR; average = 2.7 wt.% via SIMS). The higher CO2 trapped in sanidine-hosted melt inclusions may suggest higher trapping pressures than are recorded by quartz, whereas the low H2O recorded by sanidine may signify preferential H loss from sanidine. SIMS and Laser-Ablation ICP-MS (LA-ICP-MS) trace element analyses of melt inclusions define a continuous liquid line of descent from sanidine-hosted inclusions that record high Sr and increasing Ba with crystallization, to quartz-hosted inclusions that record low Sr and decreasing Ba with crystallization. In the case of the Tara magmatic system, sanidine-hosted inclusions seem to record an earlier, deeper stage of the melt's history. Assessing melt inclusions within multiple phenocryst hosts may provide insights into different stages of a melt's history from storage to ascent and eruption.

  9. Partitioning behavior of chlorine and fluorine in the system apatite melt fluid. II: Felsic silicate systems at 200 MPa

    NASA Astrophysics Data System (ADS)

    Webster, James D.; Tappen, Christine M.; Mandeville, Charles W.

    2009-02-01

    Hydrothermal experiments were conducted to determine the partitioning of Cl between rhyolitic to rhyodacitic melts, apatite, and aqueous fluid(s) and the partitioning of F between apatite and these melts at ca. 200 MPa and 900-924 °C. The number of fluid phases in our experiments is unknown; they may have involved a single fluid or vapor plus saline liquid. The partitioning behavior of Cl between apatite and melt is non-Nernstian and is a complex function of melt composition and the Cl concentration of the system. Values of DClapat/melt (wt. fraction of: Cl in apatite/Cl in melt) vary from 1 to 4.5 and are largest when the Cl concentrations of the melt are at or near the Cl-saturation value of the melt. The Cl-saturation concentrations of silicate melts are lowest in evolved, silica-rich melts, so with elevated Cl concentrations in a system and with all else equal, the maximum values of DClapat/melt occur with the most felsic melt. In contrast, values of DFapat/melt range from 11 to 40 for these felsic melts, and many of these are an order of magnitude greater than those applying to basaltic melts at 200 MPa and 1066-1150 °C. The Cl concentration of apatite is a simple and linear function of the concentration of Cl in fluid. Values of DClfluid/apat for these experiments range from 9 to 43, and some values are an order of magnitude greater than those determined in 200-MPa experiments involving basaltic melts at 1066-1150 °C. In order to determine the concentrations and interpret the behavior of volatile components in magmas, the experimental data have been applied to the halogen concentrations of apatite grains from chemically evolved rocks of Augustine volcano, Alaska; Krakatau volcano, Indonesia; Mt. Pinatubo, Philippines; Mt. St. Helens, Washington; Mt. Mazama, Oregon; Lascar volcano, Chile; Santorini volcano, Greece, and the Bishop Tuff, California. The F concentrations of these magmas estimated from apatite-melt equilibria range from 0.06 to 0.12 wt% and are

  10. Silicic Melt Generation, Segregation, and Injection by Dolerite Partial Melting of Granitic Wall Rock, McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Hersum, T. G.; Simon, A. C.; Marsh, B. D.

    2005-12-01

    Numerous, long (100's m), thin (< 30 cm), interconnected fine-grained granitic dikes cut Ferrar dolerite sills in the McMurdo Dry Valleys. The source of at least one dike is completely exposed at the upper contact of the Basement Sill and granite country rock. The dike emanates from a thin (5 cm) melt sheet separating chilled dolerite from partially melted granite. Residual interstitial granophyric melt decreases away from the contact from 55% to zero within a distance of < 20 m. Higher than expected dolerite contact temperatures of 900-950°C calculated using two-pyroxene thermometry suggest that the dolerite feeder acted as an open conduit for sustained flux of magma. As a consequence of this flow, the contact temperature was pinned above the `dry' granite minimum, the most restrictive condition necessary to generate granitic melt. Although closed-system partial melting of granite clearly occurred beyond 50 cm from the dolerite chilled margin, compositional moment balances on the feldspar ternary between the orthoclase-enriched melt sheet and granite dike whole-rock compositions are reconciled by melts segregated from increasingly orthoclase-depleted partially melted granite at 12.3 cm and closer to the dolerite chilled margin. Melting models and mass balance calculations predict a range of between 48 to 83% maximum volumes of segregated granitic melt, but these are only estimates as the samples are not exclusively residuum. If granitic melt segregation occurs by viscous compaction of the restitic crystal matrix, then, employing commonly used properties, the compaction length scale is ~3 m. This is an upper bound as the compaction model assumes constant melt fraction, but the result is nevertheless only an order of magnitude larger than the distance over which the partially melted granite has a composition that differs from unmelted granite. Contraction attending cessation of doleritic magma flow and dolerite solidification likely generated deviatoric stresses

  11. Dependence of Ru2O3 Activity on Composition of Silicate Melts: Using Statistical Correlations to Infer Thermodynamic Behavior in the Melt

    NASA Technical Reports Server (NTRS)

    Colson, R. O.; Malum, K. M.

    2005-01-01

    Understanding variations in activity with composition is an essential step in improving prediction of partition coefficients during magma evolution. Variations in activity with composition are complex and do not generally exhibit ideal behavior relative to a traditional melt-component set. Although deviations from component ideality can be modeled numerically by simply fitting to compositional variables (such as in a regular or subregular solution model), such models have not been particularly successful for describing variations in trace component activities. A better approach might be to try to identify components that do a better job of describing the behavior of the species in the melt. Electrochemical Measurement of Ru2O3 activities: Electrodes were inserted into silicate melt beads of various compositions (Table 1) suspended on Ptwire loops in a 1-atm gas mixing furnace. An electrical potential was imposed between the electrodes, the imposed potential increasing along a step ramp with a pulse imposed on each step (Fig. 1). Current flows between electrodes when electroactive species in the melt are oxidized or reduced at the electrodes. The resulting current was measured at the top and bottom of the voltage pulse, and the difference (the differential current) was plotted against potential. The peak of the resulting curve is related to the activity coefficient for the particular electroactive species (Ru2O3) in the melt [1, 2, 3]. A significant part of the nonideal contribution to activity is due not to intrinsic properties of the component in the melt, but to our ignorance about the state and mixing properties of the component in the melt.

  12. Water and magmas: insights about the water solution mechanisms in alkali silicate melts from infrared, Raman, and 29Si solid-state NMR spectroscopies

    NASA Astrophysics Data System (ADS)

    Le Losq, Charles; Mysen, Bjorn O.; Cody, George D.

    2015-12-01

    Degassing of water during the ascent of hydrous magma in a volcanic edifice produces dramatic changes in the magma density and viscosity. This can profoundly affect the dynamics of volcanic eruptions. The water exsolution history, in turn, is driven by the water solubility and solution mechanisms in the silicate melt. Previous studies pointed to dissolved water in silicate glasses and melts existing as molecules (H2Omol species) and hydroxyl groups, OH. These latter OH groups commonly are considered bonded to Si4+ but may form other bonds, such as with alkali or alkaline-earth cations, for instance. Those forms of bonding influence the structure of hydrous melts in different ways and, therefore, their properties. As a result, exsolution of water from magmas may have different eruptive consequences depending on the initial bonding mechanisms of the dissolved water. However, despite their importance, the solution mechanisms of water in silicate melts are not clear. In particular, how chemical composition of melts affects water solubility and solution mechanism is not well understood. In the present experimental study, components of such information are reported via determination of how water interacts with the cationic network of alkali (Li, Na, and K) silicate quenched melts. Results from 29Si single-pulse magic-angle spinning nuclear magnetic resonance (29Si SP MAS NMR), infrared, and Raman spectroscopies show that decreasing the ionic radius of alkali metal cation in silicate melts results in decreasing fraction of water dissolved as OH groups. The nature of OH bonding also changes as the alkali ionic radius changes. Therefore, as the speciation and bonding of water controls the degree of polymerization of melts, water will have different effects on the transport properties of silicate melts depending on their chemical composition. This conclusion, in turn, may affect volcanic phenomena related to the viscous relaxation of hydrous magmas, such as for instance the

  13. Molecular structure, configurational entropy and viscosity of silicate melts: link through the Adam and Gibbs theory of viscous flow

    NASA Astrophysics Data System (ADS)

    Le Losq, Charles; Neuville, Daniel R.

    2016-04-01

    The rheological and thermodynamic properties of silicate melts played a crucial role in the formation and the evolution of the Earth. For instance, they influenced the evolution of a plausible primordial magma ocean, and, as a result, the differentiation of the Earth mantle and crust. Further, they control the dynamic of volcanic eruptions. Because of that, modelling the viscosity or the heat capacity of silicate melts is crucial in order to model the physical processes they are involved in. The Adam and Gibbs theory of viscous flow offers a thermodynamic framework that assumes that the viscosity η (Pa s) at a temperature T (K) of a melt can be expressed as: log(η) = A + ----Be--- e T Sconf(T) (1) with Ae a pre-exponential constant related to the viscosity at infinite temperature, Be (J mol‑1) a constant proportional to the potential energy barrier opposed to the cooperative rearrangement of the liquid structure and Sconf(T) (J mol‑1 K‑1) the melt configurational entropy. With expressing Sconf(T) as the sum of the residual entropy of the glass and of the variation in melt configurational heat capacity, it is possible to link existing thermodynamic and viscosity data for melts with various chemical composition, e.g., SiO2, NaAlSi3O8 or CaAl2Si2O8. Further, it also is possible to describe the viscosity variation induced by mixing Ca and Mg or Na and K in silicate melts, under the assumption that such mixing produces an ideal excess entropy of mixing. An interesting point in the Adam and Gibbs framework is that it assumes that viscous flow occurs through the cooperative re-arrangement of molecular sub-regions in the melt. From high temperature 29Si NMR and Raman spectroscopy data, it actually is known that viscous flow occurs because of the cooperative exchange of oxygen atoms between tetrahedral SiO2 units, allowing their motions. Therefore, it is tempting to link such structural knowledge to heat capacity and viscosity data through the use of equation 1. In

  14. Eclogite-associated potassic silicate melts and chloride-rich fluids in the mantle: a possible connection

    NASA Astrophysics Data System (ADS)

    Safonov, O.; Butvina, V.

    2009-04-01

    Relics of potassium-rich (4-14 wt. % of K2O and K2O/Na2O > 1.0) melts are a specific features of some partially molten diamondiferous eclogite xenoliths in kimberlites worldwide [1, 2]. In addition, potassic silicic melt inclusions with up to 16 wt. % of K2O are associated with eclogite phases in kimberlitic diamonds (O. Navon, pers. comm.). According to available experimental data, no such potassium contents can be reached by "dry" and hydrous melting of eclogite. These data point to close connection between infiltration of essentially potassic fluids, partial melting and diamond formation in mantle eclogites [2]. Among specific components of these fluids, alkali chlorides, apparently, play an important role. This conclusion follows from assemblages of the melt relics with chlorine-bearing phases in eclogite xenoliths [1], findings of KCl-rich inclusions in diamonds from the xenoliths [3], and concentration of Cl up to 0.5-1.5 wt. % in the melt inclusions in diamonds. In this presentation, we review our experimental data on reactions of KCl melts and KCl-bearing fluids with model and natural eclogite-related minerals and assemblages. Experiments in the model system jadeite(±diopside)-KCl(±H2O) at 4-7 GPa showed that, being immiscible, chloride liquids provoke a strong K-Na exchange with silicates (jadeite). As a result, low-temperature ultrapotassic chlorine-bearing (up to 3 wt. % of Cl) aluminosilicate melts form. These melts is able to produce sanidine, which is characteristic phase in some partially molten eclogites. In addition, in presence of water Si-rich Cl-bearing mica (Al-celadonite-phlogopite) crystallizes in equilibrium with sanidine and/or potassic melt and immiscible chloride liquid. This mica is similar to that observed in some eclogitic diamonds bearing chloride-rich fluid inclusions [4], as well as in diamonds in partially molten eclogites [2]. Interaction of KCl melt with pyrope garnet also produce potassic aluminosilicate melt because of high

  15. Surface tension of natural silicate melts from 1,200-1,500 C and implications for melt structure

    NASA Technical Reports Server (NTRS)

    Walker, D.; Mullins, O., Jr.

    1981-01-01

    The surface tension between silicate liquid and gas is measured for four lava compositions (limburgite to andesite) from 1,200 to 1,500 C. It is noted that the magnitude of surface tension (gamma) is in the range 350-370 dynes/cm. Variations found in gamma as a function of liquid composition are small and have no obvious relation to liquid composition. Gamma is also found to vary little with furnace atmosphere - air, Ar, CO2, H2, CO and their mixtures. It is found that a relaxation time of hours to days, depending on temperature, is required before reproducible results can be obtained from originally crystalline starting material. The reproducible temperature dependence of gamma for complex silicate liquid solution is found to be small, positive, and a relatively simple function of liquid composition.

  16. Coordinated Hard Sphere Mixture (CHaSM): A fast approximate model for oxide and silicate melts at extreme conditions

    NASA Astrophysics Data System (ADS)

    Wolf, A. S.; Asimow, P. D.; Stevenson, D. J.

    2015-12-01

    Recent first-principles calculations (e.g. Stixrude, 2009; de Koker, 2013), shock-wave experiments (Mosenfelder, 2009), and diamond-anvil cell investigations (Sanloup, 2013) indicate that silicate melts undergo complex structural evolution at high pressure. The observed increase in cation-coordination (e.g. Karki, 2006; 2007) induces higher compressibilities and lower adiabatic thermal gradients in melts as compared with their solid counterparts. These properties are crucial for understanding the evolution of impact-generated magma oceans, which are dominated by the poorly understood behavior of silicates at mantle pressures and temperatures (e.g. Stixrude et al. 2009). Probing these conditions is difficult for both theory and experiment, especially given the large compositional space (MgO-SiO2-FeO-Al2O3-etc). We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme P-T conditions (Wolf et al., 2015). The Coordinated Hard Sphere Mixture (CHaSM) extends the Hard Sphere mixture model, accounting for the range of coordination states for each cation in the liquid. Using approximate analytic expressions for the hard sphere model, this fast statistical method compliments classical and first-principles methods, providing accurate thermodynamic and structural property predictions for melts. This framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide P-T range. Typical Mg-coordination numbers are predicted to evolve continuously from 5.25 (0 GPa) to 8.5 (250 GPa), comparing favorably with first-principles Molecular Dynamics (MD) simulations. We begin extending the model to a simplified mantle chemistry using empirical potentials (generally accurate over moderate pressure ranges, <~30 GPa), yielding predictions rooted in statistical representations of melt structure

  17. Experimental Partitioning of Chalcophile Elements between Mantle Silicate Minerals and Basaltic Melt at High Pressures and Temperatures - Implications for Sulfur Geochemistry of Mantle and Crust

    NASA Astrophysics Data System (ADS)

    Dasgupta, R.; Jego, S.; Ding, S.; Li, Y.; Lee, C. T.

    2015-12-01

    The behavior of chalcophile elements during mantle melting, melt extraction, and basalt differentiation is critical for formation of ore deposits and geochemical model and evolution of crust-mantle system. While chalcophile elements are strongly partitioned into sulfides, their behavior with different extent of melting, in particular, in the absence of sulfides, can only be modeled with complete knowledge of the partitioning behavior of these elements between dominant mantle minerals and basaltic melt with or without dissolved sulfide (S2-). However, experimental data on mineral-melt partitioning are lacking for many chalcophile elements. Crystallization experiments were conducted at 3 GPa and 1450-1600 °C using a piston cylinder and synthetic silicate melt compositions similar to low-degree partial melt of peridotite. Starting silicate mixes doped with 100-300 ppm of each of various chalcophile elements were loaded into Pt/graphite double capsules. To test the effect of dissolved sulfur in silicate melt on mineral-melt partitioning of chalcophile elements, experiments were conducted on both sulfur-free and sulfur-bearing (1100-1400 ppm S in melt) systems. Experimental phases were analyzed by EPMA (for major elements and S) and LA-ICP-MS (for trace elements). All experiments produced an assemblage of cpx + melt ± garnet ± olivine ± spinel and yielded new partition coefficients (D) for Sn, Zn, Mo, Sb, Bi, Pb, and Se for cpx/melt, olivine/melt, and garnet/melt pairs. Derived Ds (mineral/basalt) reveal little effect of S2- in the melt on mineral-melt partition coefficients of the measured chalcophile elements, with Ds for Zn, Mo, Bi, Pb decreasing by less than a factor of 2 from S-free to S-bearing melt systems or remaining similar, within error, between S-free and S-bearing melt systems. By combining our data with existing partitioning data between sulfide phases and silicate melt we model the fractionation of these elements during mantle melting and basalt

  18. Metal/sulfide-silicate intergrowth textures in EL3 meteorites: Origin by impact melting on the EL parent body

    NASA Astrophysics Data System (ADS)

    van Niekerk, Deon; Keil, Klaus

    2011-10-01

    We document the petrographic setting and textures of Fe,Ni metal, the mineralogy of metallic assemblages, and the modal mineral abundances in the EL3 meteorites Asuka (A-) 881314, A-882067, Allan Hills 85119, Elephant Moraine (EET) 90299/EET 90992, LaPaz Icefield 03930, MacAlpine Hills (MAC) 02635, MAC 02837/MAC 02839, MAC 88136, Northwest Africa (NWA) 3132, Pecora Escarpment 91020, Queen Alexandra Range (QUE) 93351/QUE 94321, QUE 94594, and higher petrologic type ELs Dar al Gani 1031 (EL4), Sayh al Uhaymir 188 (EL4), MAC 02747 (EL4), QUE 94368 (EL4), and NWA 1222 (EL5). Large metal assemblages (often containing schreibersite and graphite) only occur outside chondrules and are usually intergrown with silicate minerals (euhedral to subhedral enstatite, silica, and feldspar). Sulfides (troilite, daubréelite, and keilite) are also sometimes intergrown with silicates. Numerous authors have shown that metal in enstatite chondrites that are interpreted to have been impact melted contains euhedral crystals of enstatite. We argue that the metal/sulfide-silicate intergrowths in the ELs we studied were also formed during impact melting and that metal in EL3s thus does not retain primitive (i.e., nebular) textures. Likewise, the EL4s are also impact-melt breccias. Modal abundances of metal in the EL3s and EL4s range from approximately 7 to 30 wt%. These abundances overlap or exceed those of EL6s, and this is consistent either with pre-existing heterogeneity in the parent body or with redistribution of metal during impact processes.

  19. Impact of Melt Segregation on Genesis of Intermediate and Silicic Magmas in Deep Crustal Hot Zones

    NASA Astrophysics Data System (ADS)

    Solano, J.; Jackson, M.; Sparks, R. S.; Blundy, J.

    2009-12-01

    The evolution of a system in which hot magmatic sills are repeatedly intruded into cool country rock at depth in the crust is modelled in one dimension. The model couples that of Annen et al. (2002), describing heat transfer and phase change during repeated sill intrusions, with that of Jackson et al. (2003), describing heat transfer, phase change and associated buoyancy driven melt segregation and compaction of the solid matrix following a single sill intrusion. The aim of the work is to investigate the impact of melt segregation on melt fraction and composition during repeated sill intrusions in deep crustal hot zones. The model developed uses an enthalpy based method whilst solving for temperature. This allows complex melting behaviour, including isothermal and non-linear relations, to be parameterised and included. The emplacement of hot, mantle-derived basaltic sills causes the pre-existing country rock to warm, which allows later sills to remain partially molten over timescales which are long enough to facilitate melt segregation processes. At fast emplacement rates, a large partially molten zone is generated above the intrusions into which melt can percolate, leading to the generation of high porosity melt lenses which can mobilise and form magmas. At slower emplacement rates, the hot zone evolves differently depending upon whether the intruded sills accumulate by over- or under-accretion. Under-accretion of sills does not produce a large partially molten zone in the overlying country rock, so the melt is contained within the intrusion zone. Over-accretion continues to melt the overlying country rock for all emplacement rates. Two types of melt are present in the system, crustal melt formed via partial melting, and residual melt formed from the crystallisation of the intruded basalt. The mobilised magmas comprise varying degrees of crustal and residual melts which, alongside with temperature and depth of melting, will determine their composition. The process

  20. Partitioning of elements between silicate melt and immiscible fluoride, chloride, carbonate, phosphate and sulfate melts, with implications to the origin of natrocarbonatite

    NASA Astrophysics Data System (ADS)

    Veksler, Ilya V.; Dorfman, Alexander M.; Dulski, Peter; Kamenetsky, Vadim S.; Danyushevsky, Leonid V.; Jeffries, Teresa; Dingwell, Donald B.

    2012-02-01

    Liquid-liquid partitioning of 42 elements between synthetic silicate melts and immiscible fluoride, chloride, carbonate, phosphate and sulfate liquids was studied at temperatures of 650-1100 °C, pressures 72-100 MPa, with 0-11 wt.% H2O. One series of experiments was performed in a rotating internally-heated autoclave where separation of the immiscible liquids was assisted by centrifugal forces. An analogous series of experiments was done in static rapid-quench cold-seal pressure vessels. The experimentally determined liquid-liquid distribution coefficients (D's) vary over several orders of magnitude, as a result of variable Coulombic interactions between cations and anions. For alkaline, alkaline earth and rare earth elements ther is a strong and systematic dependence of the liquid/liquid D values on the ionic potential Z/r for all the examined systems. In contrast, highly charged cations (e.g., HFSE) show no systematic relationships between the D's and Z/r. New experimental constraints on the carbonate/silicate liquid-liquid D values presented here confirm that rare metals such as Nb, Zr, REE, Th and U concentrate in silicate liquids, and therefore carbonatites that carry economical rare metal mineralization are not likely to have formed by liquid immiscibility. The comparison between experimentally-determined carbonate-silicate liquid-liquid D values and bulk-rock natrocarbonatite vs. nephelinite compositions at the Oldoinyo Lengai in Tanzania reveals significant discrepancies for Cs, Rb, Ba, Be, Zn, heavy REE, Ti, Mo and W, thus rendering a simple, one-stage immiscibility model for Oldoinyo Lengai questionable.

  1. Coordinated Hard Sphere Mixture (CHaSM): A simplified model for oxide and silicate melts at mantle pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Wolf, Aaron S.; Asimow, Paul D.; Stevenson, David J.

    2015-08-01

    We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme temperatures and pressures, including deep mantle conditions like those in the early Earth magma ocean. The Coordinated Hard Sphere Mixture (CHaSM) is based on an extension of the hard sphere mixture model, accounting for the range of coordination states available to each cation in the liquid. By utilizing approximate analytic expressions for the hard sphere model, this method is capable of predicting complex liquid structure and thermodynamics while remaining computationally efficient, requiring only minutes of calculation time on standard desktop computers. This modeling framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide range of pressures and temperatures. We find that the typical coordination number of the Mg cation evolves continuously upward from 5.25 at 0 GPa to 8.5 at 250 GPa. The results produced by CHaSM are evaluated by comparison with predictions from published first-principles molecular dynamics calculations, indicating that CHaSM is accurately capturing the dominant physics controlling the behavior of oxide melts at high pressure. Finally, we present a simple quantitative model to explain the universality of the increasing Grüneisen parameter trend for liquids, which directly reflects their progressive evolution toward more compact solid-like structures upon compression. This general behavior is opposite that of solid materials, and produces steep adiabatic thermal profiles for silicate melts, thus playing a crucial role in magma ocean evolution.

  2. In Situ Determination of Viscosity and Structure of Carbonatitic to Carbonate-Silicate Melts as Function of Pressure and Temperature

    NASA Astrophysics Data System (ADS)

    Stagno, V.; Kono, Y.; Lustrino, M.; Irifune, T.

    2015-12-01

    Carbonatitic and carbonate-silicate magmas are representative of mantle-derived liquids that form by partial melting of carbonated peridotite and eclogite rocks at depths greater than 60 km in the Earth's interior. Carbonatitic melts are expected to contain 1-5 wt% SiO2, but at shallower conditions (about 100 km in depth), as a result of large melt fraction during decompression, SiO2 content increases up to 10-20 wt%. This variation in composition is expected to cause significant changes in the physical properties (e.g. viscosity and melt structure) of these magmas. The aim of this study was to determine the viscosity and structure of CO2-rich melts with variable SiO2 content representative of carbonatitic to carbonate-silicate natural melts. A mixture of CaCO3, MgCO3, SiO2, FeO, and NaCl was used as starting material. Synthetic glasses with 5 wt% and 18wt% SiO2 were quenched at high pressure using multi anvil presses. Viscosity measurements on CO2-bearing liquids were conducted with the falling-sphere method using the Paris-Edinburg type large volume apparatus at pressures between 1.5-6 GPa and temperatures of 1100-1500 °C. Determinations of viscosity of these liquids were determined from radiographic images recorded with a high-speed camera installed at Sector 16-BM-B (APS, Argonne). Falling velocity of the platinum probing spheres was measured by ultrafast X-ray radiography using a high-speed camera with a 500 fps recording rate (exposure time of 2 ms). The viscosity was, then, calculated from the Stokes equation including the correction factors for the effect of the wall and the end effect (Kono et al. 2014). Structural measurements of the liquid at high temperature were also performed using multi-angle energy dispersive X-ray diffraction technique. Preliminary results from this study will contribute to understand the variation of viscosity as function of pressure, temperature and degree of polymerization of CO2- melts during up welling within the

  3. Effects of temperature, silicate melt composition, and oxygen fugacity on the partitioning of V, Mn, Co, Ni, Cu, Zn, As, Mo, Ag, Sn, Sb, W, Au, Pb, and Bi between sulfide phases and silicate melt

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Audétat, Andreas

    2015-08-01

    In order to assess the role of sulfide in controlling the ore metal budgets and fractionation during magmatic genesis and differentiation, the partition coefficients (D) of V, Mn, Co, Ni, Cu, Zn, As, Mo, Ag, Sn, Sb, W, Au, Pb, and Bi between sulfide liquid (SL), monosulfide solid solution (MSS), and basaltic to rhyolitic melts (SM) were determined at 900-1200 °C, 0.5-1.5 GPa, and oxygen fugacity (fO2) ranging from ∼FMQ-2 to FMQ+3, in a piston-cylinder apparatus. The DSL/SM values range from 0.4 to 2 for V, 0.5 to 3 for Mn, 80 to 580 for Co, 2300 to 18,000 for Ni, 800 to 4600 for Cu, 1 to 11 for Zn, 20 to 180 for As, 4 to 230 for Mo, 450 to 1600 for Ag, 5 to 24 for Sn, 10 to 80 for Sb, 0.03 to 0.16 for W, 2000 to 29,000 for Au, 24 to 170 for Pb, and 830 to 11,000 for Bi; whereas the DMSS/SM values range from 0.04 to 10 for V, 0.5 to 10 for Mn, 70 to 2500 for Co, 650 to 18,000 for Ni, 280 to 42,000 for Cu, 0.1 to 80 for Zn, 0.2 to 30 for As, 1 to 820 for Mo, 20 to 500 for Ag, 0.2 to 220 for Sn, 0.1 to 40 for Sb, 0.01 to 24 for W, 10 to 2000 for Au, 0.03 to 6 for Pb, and 1 to 350 for Bi. Both DMSS/SM and DSL/SM values generally increase with decreasing temperature or decreasing FeOtot content in silicate melt, except for Mo, DMSS/SM and DSL/SM of which show a clear decrease with decreasing temperature. At given temperature and FeOtot content, high oxygen fugacity appears to lead to a significant decrease in DMSS/SM of Au, Bi, Mo, and potentially As. The partitioning data obtained experimentally in this study and previous studies were fitted to an empirical equation that expresses the DMSS/SM and/or DSL/SM of a given element as a function of temperature, oxygen fugacity, and FeOtot content of the silicate melt: log (DSL/SMorDMSS/SM = d + a · 10, 000 / T + b · (ΔFMQ) + c · log (FeOmelt) in which T is temperature in K, FeOmelt denotes wt% FeOtot in silicate melt, and ΔFMQ denotes log fO2 relative to the fayalite-magnetite-quartz (FMQ) oxygen buffer. The

  4. Bubbles Accumulation And Their Role On The Eruptability Of Melt-Rich Silicic Lenses In Upper Crustal Magma Reservoirs

    NASA Astrophysics Data System (ADS)

    Parmigiani, A.; Faroughi, S. A.; Huber, C.; Bachmann, O.

    2014-12-01

    A first-order observation in magmatic rocks is that highly evolved rhyolites are relatively abundant in the volcanic realm, but their plutonic counterparts (granites sensu stricto) are rarer, when ratioed to dacitic/granodioritic compositions. As eruptability is a function of the buoyancy of magmas in upper crustal reservoirs, the presence of exsolved gas (bubbles) plays a fundamental role on eruptability by lowering the bulk density of magmas. Then, if exsolved gas content can accumulate in certain areas of magma reservoirs, it follows that such areas might be more prone to erupt. Magma reservoirs in the upper crust likely have relatively stable, sharp transitions in crystallinity between crystal-rich regions and crystal-poor regions. With this framework in mind, in this presentation, by means of theoretical considerations, numerical modelling and laboratory experiments, we suggest that the storage capacity of exsolved gas in magma reservoirs is a function of the relative abundance of melt respect to crystals present; crystal-poor regions (high melt to crystal volume ratio) tend to act as sponges, accumulating bubbles, while crystal-rich regions (mush zones with low melt to crystal ratio) tend to degas efficiently, leading to upward percolation of volatiles. Hence, melt-rich cupolas accumulating in upper parts of crystal-rich upper crustal reservoirs are particularly eruptible and dominate the volume of volcanic deposits in silicic magmatic provinces.

  5. Internally consistent mineral solubility and hydrous melting relations for simple silicate-H2O systems and their significance

    NASA Astrophysics Data System (ADS)

    Hack, A. C.; Hermann, J.; Mavrogenes, J. A.

    2005-12-01

    Mineral solubility and melting relations in the systems SiO2-H2O, NaAlSi3O8(albite)-H2O and MgO-SiO2-H2O have been the subject of many experimental studies. This is a direct reflection of their importance as analogues for crust and mantle rock types, and as guides to the behavior of more complex silicate-H2O systems. A particularly interesting feature of all of these systems is that the wet solidus is known to terminate with increasing pressure (the so-called second critical point). The nature of fluids that occur above the wet solidus is a source of considerable confusion but is of key importance if certain ultra-high pressure localities and subduction processes are to be understood. Although none of these simple systems has been completely explored experimentally we have critically evaluated and assimilated the information available from each to construct a general and internally consistent PTX description of phase relations and solubility in silicate-H2O systems. It is presented as a series of PTX projections. We identify two possible end members in a continuum of phase relation topologies for silicate-H2O, and show that these result from seemingly minor but important differences in the compositional behavior of silicate melt coexisting with H2O-rich fluid. The analysis bears directly on the nature of high pressure magma genesis and degassing histories. We also consider mineral-buffered supercritical fluid, elucidate the PT region in which this phenomenon occurs for different rock-types, its relation to subsolidus mineral solubility isopleths, aqueous vapor-saturated and the dry liquidus curves and general compositional behavior. We argue that mineral-saturated fluids at pressures above the second critical point are compositionally well defined and that fluid compositions and physical properties are strongly temperature dependent. Fluids occurring in the continental crust should remain in the dilute supercritical aqueous fluid regime and likewise subsolidus

  6. Estimation of trace element concentrations in the lunar magma ocean using mineral- and metal-silicate melt partition coefficients

    NASA Astrophysics Data System (ADS)

    Sharp, Miriam; Righter, Kevin; Walker, Richard J.

    2015-04-01

    This study uses experimentally determined plagioclase-melt D values to estimate the trace element concentrations of Sr, Hf, Ga, W, Mo, Ru, Pd, Au, Ni, and Co in a crystallizing lunar magma ocean at the point of plagioclase flotation. Similarly, experimentally determined metal-silicate partition experiments combined with a composition model for the Moon are used to constrain the concentrations of W, Mo, Ru, Pd, Au, Ni, and Co in the lunar magma ocean at the time of core formation. The metal-silicate derived lunar mantle estimates are generally consistent with previous estimates for the concentration of these elements in the lunar mantle. Plagioclase-melt derived concentrations for Sr, Ga, Ru, Pd, Au, Ni, and Co are also consistent with prior estimates. Estimates for Hf, W, and Mo, however, are higher. These elements may be concentrated in the residual liquid during fractional crystallization due to their incompatibility. Alternatively, the apparent enrichment could reflect the inappropriate use of bulk anorthosite data, rather than data for plagioclase separates.

  7. Metal-Silicate Partitioning of Bi, In, and Cd as a Function of Temperature and Melt Composition

    NASA Technical Reports Server (NTRS)

    Marin, Nicole; Righter, K.; Danielson, L.; Pando, K.; Lee, C.

    2013-01-01

    The origin of volatile elements in the Earth, Moon and Mars is not known; however, several theories have been proposed based on volatile elements such as In, As, Se, Te and Zn which are in lower concentration in the Earth, Moon, and Mars than in chondrites. Explanations for these low concentrations are based on two contrasting theories for the origin of Earth: equilibrium core formation versus late accretion. One idea is that the volatiles were added during growth of the planets and Moon, and some mobilized into the metallic core while others stayed in the mantle (e.g., [1]). The competing idea is that they were added to the mantles after core formation had completed (e.g., [2]). Testing these ideas involves quantitative modeling which can only be performed after data is obtained on the systematic metal-silicate partitioning behavior of volatile elements with temperature, pressure and melt composition. Until now, such data for Bi, In, and Cd has been lacking. After conducting a series of high pressure, high temperature experiments, the metal-silicate partition coefficients of Bi, In, and Cd as a function of temperature and melt composition can be used to evaluate potential conditions under which terrestrial planets differentiated into core and mantle, and how they acquired volatiles.

  8. Carbon solution and partitioning between metallic and silicate melts in a shallow magma ocean: Implications for the origin and distribution of terrestrial carbon

    NASA Astrophysics Data System (ADS)

    Dasgupta, Rajdeep; Chi, Han; Shimizu, Nobumichi; Buono, Antonio S.; Walker, David

    2013-02-01

    The origin of bulk silicate Earth carbon inventory is unknown and the fate of carbon during the early Earth differentiation and core formation is a missing link in the evolution of the terrestrial carbon cycle. Here we present high pressure (P)-temperature (T) experiments that offer new constraints upon the partitioning of carbon between metallic and silicate melt in a shallow magma ocean. Experiments were performed at 1-5 GPa, 1600-2100 °C on mixtures of synthetic or natural silicates (tholeiitic basalt/alkali basalt/komatiite/fertile peridotite) and Fe-Ni-C ± Co ± S contained in graphite or MgO capsules. All the experiments produced immiscible Fe-rich metallic and silicate melts at oxygen fugacity (fO2) between ˜IW-1.5 and IW-1.9. Carbon and hydrogen concentrations of basaltic glasses and non-glassy quenched silicate melts were determined using secondary ionization mass spectrometry (SIMS) and speciation of dissolved C-O-H volatiles in silicate glasses was studied using Raman spectroscopy. Carbon contents of metallic melts were determined using both electron microprobe and SIMS. Our experiments indicate that at core-forming, reduced conditions, carbon in deep mafic-ultramafic magmas may dissolve primarily as various hydrogenated species but the total carbon storage capacity, although is significantly higher than solubility of CO2 under similar conditions, remains low (<500 ppm). The total carbon content in our reduced melts at graphite saturation increases with increasing melt depolymerization (NBO/T), consistent with recent spectroscopic studies, and modestly with increasing hydration. Carbon behaves as a metal-loving element during core-mantle separation and our experimental DCmetal/silicate varies between ˜4750 and ⩾150 and increases with increasing pressure and decreases with increasing temperature and melt NBO/T. Our data suggest that if only a trace amount of carbon (˜730 ppm C) was available during early Earth differentiation, most of it was

  9. Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS. Part 2: application to Taupo Volcanic Zone rhyolites

    NASA Astrophysics Data System (ADS)

    Bégué, Florence; Gualda, Guilherme A. R.; Ghiorso, Mark S.; Pamukcu, Ayla S.; Kennedy, Ben M.; Gravley, Darren M.; Deering, Chad D.; Chambefort, Isabelle

    2014-11-01

    Constraining the pressure of crystallisation of large silicic magma bodies gives important insight into the depth and vertical extent of magmatic plumbing systems; however, it is notably difficult to constrain pressure at the level of detail necessary to understand shallow magmatic systems. In this study, we use the recently developed rhyolite-MELTS geobarometer to constrain the crystallisation pressures of rhyolites from the Taupo Volcanic Zone (TVZ). As sanidine is absent from the studied deposits, we calculate the pressures at which quartz and feldspar are found to be in equilibrium with melt now preserved as glass (the quartz +1 feldspar constraint of Gualda and Ghiorso, Contrib Mineral Petrol 168:1033. doi:10.1007/s00410-014-1033-3. 2014). We use glass compositions (matrix glass and melt inclusions) from seven eruptive deposits dated between ~320 and 0.7 ka from four distinct calderas in the central TVZ, and we discuss advantages and limitations of the rhyolite-MELTS geobarometer in comparison with other geobarometers applied to the same eruptive deposits. Overall, there is good agreement with other pressure estimates from the literature (amphibole geobarometry and H2O-CO2 solubility models). One of the main advantages of this new geobarometer is that it can be applied to both matrix glass and melt inclusions—regardless of volatile saturation. The examples presented also emphasise the utility of this method to filter out spurious glass compositions. Pressure estimates obtained with the new rhyolite-MELTS geobarometer range between ~250 to ~50 MPa, with a large majority at ~100 MPa. These results confirm that the TVZ hosts some of the shallowest rhyolitic magma bodies on the planet, resulting from the extensional tectonic regime and thinning of the crust. Distinct populations with different equilibration pressures are also recognised, which is consistent with the idea that multiple batches of eruptible magma can be present in the crust at the same time and

  10. Equation of state of refractory silicate glasses and melts by high-pressure x-ray microtomography

    NASA Astrophysics Data System (ADS)

    Lesher, C. E.; Gaudio, S.; Wang, Y.; Nishiyama, N.; Rivers, M.; Tangeman, J.

    2005-12-01

    The new high-pressure x-ray tomographic microscope on 13-BM-D at GSECARS-APS/ANL is being used to determine the equation of state of glasses and melts. We demonstrate that the volume of compressed silicate glass microspheres can be measured accurately to constrain the bulk modulus and its pressure derivative up to ~6 GPa. The pressure generation system consists of two opposing Drickamer anvils compressed within an x-ray-transparent Al containment ring supported by thrust bearings and driven by a 250-ton hydraulic press. This configuration permits the pressure cell to rotate under load, while collecting 360 x-ray radiographs through 180 degrees of rotation. Individual x-ray radiographs are recorded by a CCD camera after conversion to visible light by a YAG scintillator and combined to render the volume using a back-projection algorithm and standard flat/dark field corrections with minimal filtering, following by image processing. Results are reported for two magnesium silicate glasses (33 mol % and 38 mol % SiO2) synthesized by levitation-laser heating. Vitreous forsterite (33 mol % SiO2) compressed to 4.8 GPa shows a 5% reduction in volume, while 38 mol % SiO2 glass compressed to 6.4 GPa shows an 8.7% decrease in volume - corresponding to bulk moduli of 75 and 55 GPa, respectively, for K' of 4. The differences in the compressibility of these magnesium silicate glasses are consistent with the structural differences inferred from neutron and x-ray diffraction studies. Efforts to develop a heating circuit will soon allow the recovery of thermal expansivity, central to efforts to derive a P-V-T equation of state for silicate liquids relevant to the Earth's deep interior.

  11. Energetics of silicate melts from thermal diffusion studies. Annual progress report

    SciTech Connect

    Walker, D.

    1992-07-01

    Efforts are reported in the following areas: laboratory equipment (multianvils for high P/T work, pressure media, SERC/DL sychrotron), liquid-state thermal diffusion (silicate liquids, O isotopic fractionation, volatiles, tektites, polymetallic sulfide liquids, carbonate liquids, aqueous sulfate solutions), and liquid-state isothermal diffusion (self-diffusion, basalt-rhyolite interdiffusion, selective contamination, chemical diffusion).

  12. Redox dynamics in multicomponent, iron-bearing silicate melts and glasses: Application to the float-glass processing of high-temperature silicate glassmelts

    NASA Astrophysics Data System (ADS)

    Cook, Glen Bennett

    Processing high-strain-point glasses by the float process is challenged by the relative thermochemical properties of glassmelts and the liquid-metal float medium. As the chemical reaction between the glassmelt and the float metal involves dynamic reduction of the glassmelt, this research has examined the constraints on high-temperature float processing of glassmelts by combining metal-alloy/oxide reaction thermodynamics and Wagnerian kinetic models for redox reactions in silicate melts. The dynamic response of Fe-bearing, p-type (polaronic) semiconducting amorphous silicates to a chemical potential gradient of oxygen has been shown to be rate-limited by the chemical diffusion of network-modifying cations. The persistence of this mechanism to very low Fe concentrations in Fe-doped magnesium aluminosilicate glasses was proven with Rutherford backscattering spectroscopy. Three glasses, with 0.1, 0.5, and 1.25 mol. % FeO were reacted with air at temperatures from 710-845sp°C. For all compositions and temperatures, oxidation was dominated by network modifier diffusion; an activation energy of 475 kJ*molsp{-1} characterized the process. Chemical dynamics in a high-temperature float environment were characterized on liquid-liquid reaction couples between two low-Fe sodium-aluminoborosilicate (NABS) glassmelts (0.01 and 0.08 mol. % FeO) and Au-30Sn and Au-28Ge (atomic basis) alloys. Experiments were performed in the temperature range 1250-1450sp°C for 30 min; wavelength-dispersive and Rutherford backscattering spectroscopies were employed. These exothermic liquid-metal alloys display large negative deviations from ideal solution behavior, with significantly depressed chemical activities. Diffusion of Sn or Ge in the NABS glassmelts (depth and concentration) was limited at all temperatures to levels comparable to conventional soda-lime (NCS) float glass (˜2 min on pure Sn at 1100sp°C). Incorporation of Sn or Ge was reduced significantly in the higher-Fe-content NABS

  13. The Effect of Composition and Pressure on the Structure of Carbonate-Silicate Melts Using in situ X-ray Diffuse Scattering

    NASA Astrophysics Data System (ADS)

    Hummer, D. R.; Kavner, A.; Manning, C. E.

    2013-12-01

    Carbonatites are carbon-rich magmas that make up a crucial portion of the deep-Earth carbon cycle. During transport from the site of melting, reaction with surrounding mantle and crust can cause significant changes in their carbonate-silicate ratio. However, very little is known about the structure of carbonate-silicate liquids at the high pressures and temperatures where melts originate and metasomatism occurs. To examine how the melt structure of carbonate-silicate binary systems evolves as a function of pressure and composition, we performed in situ X-ray scattering experiments in the Paris-Edinburgh press at HPCAT (Advanced Photon Source). Mixtures from the CaCO3-CaSiO3 and CaCO3-Mg2SiO4 binary systems were used to simulate mantle carbonatites with differing Si:O ratio. Samples were loaded using the experimental setup of Yamada et al [1], and held at 1800 oC and a pressure of either 3 or 6 GPa while energy dispersive X-ray scattering spectra were recorded. Spectra were collected at nine different scattering angles to achieve coverage in reciprocal space up to q = 20 Å-1. Pair distribution functions for pure calcite confirm that carbonates form a simple ionic liquid, as found by previous investigators. [2,3] The silicate portion of carbonate-silicate melts, however, is extensively chain polymerized. This polymerization occurs even in melts containing Mg2SiO4, in which the solid is completely unpolymerized. However, analysis of Si-Si distances reveals that Mg2SiO4-bearing melts likely contain shorter, more distorted chains, while CaSiO3-bearing melts form extended chains with a Si-O-Si angles close to 180o. For silicate-rich mixtures in both systems, the extent of silica polymerization (as measured by the amount of scattering at the Si-Si pair distance of 3.3 Å) moderately increases with increasing carbonate content. Comparing pair distribution functions calculated from 3 and 6 GPa data reveal that pressure moderately increases the degree of polymerization of

  14. Mixing Silicate Melts with High Viscosity Contrast by Chaotic Dynamics: Results from a New Experimental Device

    NASA Astrophysics Data System (ADS)

    de Campos, Cristina; Perugini, Diego; Ertel-Ingrisch, Werner; Dingwell, Donald B.; Poli, Giampiero

    2010-05-01

    A new experimental device has been developed to perform chaotic mixing between high viscosity melts under controlled fluid-dynamic conditions. The apparatus is based on the Journal Bearing System (JBS). It consists of an outer cylinder hosting the melts of interest and an inner cylinder, which is eccentrically located. Both cylinders can be independently moved to generate chaotic streamlines in the mixing system. Two experiments were performed using as end-members different proportions of a peralkaline haplogranite and a mafic melt, corresponding to the 1 atm eutectic composition in the An-Di binary system. The two melts were stirred together in the JBS for ca. two hours, at 1,400° C and under laminar fluid dynamic condition (Re of the order of 10-7). The viscosity ratio between the two melts, at the beginning of the experiment, was of the order of 103. Optical analyses of experimental samples revealed, at short length scale (of the order of μm), a complex pattern of mixed structures. These consisted of an intimate distribution of filaments; a complex inter-fingering of the two melts. Such features are typically observed in rocks thought to be produced by magma mixing processes. Stretching and folding dynamics between the melts induced chaotic flow fields and generated wide compositional interfaces. In this way, chemical diffusion processes become more efficient, producing melts with highly heterogeneous compositions. A remarkable modulation of compositional fields has been obtained by performing short time-scale experiments and using melts with a high viscosity ratio. This indicates that chaotic mixing of magmas can be a very efficient process in modulating compositional variability in igneous systems, especially under high viscosity ratios and laminar fluid-dynamic regimes. Our experimental device may replicate magma mixing features, observed in natural rocks, and therefore open new frontiers in the study of this important petrologic and volcanological process.

  15. Composition of silicate partial melts of carbonated pelite at 3-5 GPa and genesis of arc magma

    NASA Astrophysics Data System (ADS)

    Tsuno, K.; Dasgupta, R.; Danielson, L. R.; Righter, K.

    2012-12-01

    The composition of arc magmas reflects a complex process of slab-modified mantle wedge melting and magma differentiation in the crust. The composition of arc magma is distinct among various subduction zones owing to the different thermal structures [1] and perhaps different subduction input. Partial melts of downgoing sediment generated at slab-top or in sedimentary diapir [2] may be key in metasomatizing the mantle wedge. However, the effect of carbonates on the silicate partial melt composition of pelitic sediments is less constrained under the deep sub-arc conditions (~5 GPa). Here we provide silicate partial melt composition of Al-poor carbonated pelite to 5 GPa and discuss whether such melts may be a potential metasomatizing agent for arc source, particularly in Central America, Sunda, and Vanuatu where low-alumina carbonated pelite subduct [3]. We performed piston cylinder (3 GPa) and multianvil (4 and 5 GPa) experiments at 800-1150 °C, using a synthetic pelite with 0.5 and 1.0 wt.% H2O and 5.0 wt.% CO2. The experimental procedures and the resulting melting phase relations of this study are described in ref. [4]. The rhyolitic partial melt at 3 GPa evolves to trachydacite at 4 GPa and tephriphonolite at 5 GPa. At 3 GPa silicate partial melt compositions of our study are similar to those derived from hydrous, CO2-free pelite [e.g., 5-7], and are lower in SiO2 (63-65 wt.%) and higher in TiO2 (1-2 wt.%), MnO (~0.6 wt.%) and CaO (2-9 wt.%) at 4 GPa. At 5 GPa and 1050-1100 °C immiscible silicate melts, in the presence of carbonatitic melt, are even more distinct in terms of SiO2 (51-55 wt.%), TiO2 (~2-3 wt.%), Al2O3 (~10-12 wt.%), FeO* (~5-9 wt.%), MnO (0.1-0.3 wt.%), and CaO (~11-14 wt.%) compared to pelite partial melts in the absence of CO2 (~69-74 wt.% SiO2, 0.5-1.0 wt.% TiO2, ~12-15 wt.% Al2O3, ~1 wt.% FeO*, ~0.1 wt.% MnO, and 0.3-0.9 wt.% CaO). The compositions of Central America, Sunda, and Vanuatu arc basalts, at 5-15 wt.% MgO, are richer in FeO*, Mn

  16. Contrasting Effects of Carbon and Sulfur on Fe-Isotope Fractionation between Metal and Silicate Melt during Planetary Core Formation

    NASA Astrophysics Data System (ADS)

    Elardo, S. M.; Shahar, A.

    2015-12-01

    There are numerous studies that show well-resolved Fe isotope fractionations in igneous materials from different planetary bodies. Potential explanations for these fractionations include a non-chondritic bulk planetary Fe isotopic composition, and equilibrium fractionation between Fe-alloys or minerals and silicate melts during planetary differentiation, mantle melting, or fractional crystallization. This is further complicated by the fact that these processes are not mutually exclusive, making the interpretation of Fe isotope data a complex task. Here we present new experimental results investigating the effect of C on Fe isotope fractionation between molten peridotite and an Fe-alloy. Experiments were conducted at 1 GPa and 1850° C for 0.5 - 3 hours on a mixture of an 54Fe-spiked peridotite and Fe-metal with and without Ni metal in an end-loaded piston cylinder at the Geophysical Laboratory. Carbon saturation was achieved with a graphite capsule, and resulted in C contents of the Fe-alloy in our experiments ranging from 3.8 - 4.9 wt. %. The metal and silicate phases from half of each experiment were separated manually and dissolved in concentrated acids. Iron was separated from matrix elements by anion exchange chromatagraphy. Iron-isotopic compositions were determined with the Nu Plasma II MC-ICP-MS at GL. The other half of each experiment was used for quantitative microbeam analysis. Equilibrium was assessed with a time series and the three-isotope exchange method. The Ni-free experiments resulted in no resolvable Fe isotope fractionation between the Fe-C-alloy and molten silicate. This is in contrast to the results of Shahar et al. (2015) which showed a fractionation for Δ57Fe of ~0.18 ‰ between a peridotite and an Fe-alloy with a similar S abundance to C in these experiments. The one experiment thus far that contained Ni (~4 wt. % in the alloy) showed a resolvable fractionation between the Fe-Ni-C alloy and silicate of ~0.10 ‰. Shahar et al. found a

  17. A thermodynamical model for the surface tension of silicate melts in contact with H2O gas

    USGS Publications Warehouse

    Colucci, Simone; Battaglia, Maurizio; Trigila, Raffaello

    2016-01-01

    Surface tension plays an important role in the nucleation of H2O gas bubbles in magmatic melts and in the time-dependent rheology of bubble-bearing magmas. Despite several experimental studies, a physics based model of the surface tension of magmatic melts in contact with H2O is lacking. This paper employs gradient theory to develop a thermodynamical model of equilibrium surface tension of silicate melts in contact with H2O gas at low to moderate pressures. In the last decades, this approach has been successfully applied in studies of industrial mixtures but never to magmatic systems. We calibrate and verify the model against literature experimental data, obtained by the pendant drop method, and by inverting bubble nucleation experiments using the Classical Nucleation Theory (CNT). Our model reproduces the systematic decrease in surface tension with increased H2O pressure observed in the experiments. On the other hand, the effect of temperature is confirmed by the experiments only at high pressure. At atmospheric pressure, the model shows a decrease of surface tension with temperature. This is in contrast with a number of experimental observations and could be related to microstructural effects that cannot be reproduced by our model. Finally, our analysis indicates that the surface tension measured inverting the CNT may be lower than the value measured by the pendant drop method, most likely because of changes in surface tension controlled by the supersaturation.

  18. The solvation radius of silicate melts based on the solubility of noble gases and scaled particle theory.

    PubMed

    Ottonello, Giulio; Richet, Pascal

    2014-01-28

    The existing solubility data on noble gases in high-temperature silicate melts have been analyzed in terms of Scaling Particle Theory coupled with an ab initio assessment of the electronic, dispersive, and repulsive energy terms based on the Polarized Continuum Model (PCM). After a preliminary analysis of the role of the contracted Gaussian basis sets and theory level in reproducing appropriate static dipole polarizabilities in a vacuum, we have shown that the procedure returns Henry's law constants consistent with the values experimentally observed in water and benzene at T = 25 °C and P = 1 bar for the first four elements of the series. The static dielectric constant (ɛ) of the investigated silicate melts and its optical counterpart (ɛ(∞)) were then resolved through the application of a modified form of the Clausius-Mossotti relation. Argon has been adopted as a probe to depict its high-T solubility in melts through an appropriate choice of the solvent diameter σs, along the guidelines already used in the past for simple media such as water or benzene. The σs obtained was consistent with a simple functional form based on the molecular volume of the solvent. The solubility calculations were then extended to He, Ne, and Kr, whose dispersive and repulsive coefficients are available from theory and we have shown that their ab initio Henry's constants at high T reproduce the observed increase with the static polarizability of the series element with reasonable accuracy. At room temperature (T = 25 °C) the calculated Henry's constants of He, Ne, Ar, and Kr in the various silicate media predict higher solubilities than simple extrapolations (i.e., Arrhenius plots) based on high-T experiments and give rise to smooth trends not appreciably affected by the static polarizabilities of the solutes. The present investigation opens new perspectives on a wider application of PCM theory which can be extended to materials of great industrial interest at the core of

  19. The solvation radius of silicate melts based on the solubility of noble gases and scaled particle theory

    SciTech Connect

    Ottonello, Giulio; Richet, Pascal

    2014-01-28

    The existing solubility data on noble gases in high-temperature silicate melts have been analyzed in terms of Scaling Particle Theory coupled with an ab initio assessment of the electronic, dispersive, and repulsive energy terms based on the Polarized Continuum Model (PCM). After a preliminary analysis of the role of the contracted Gaussian basis sets and theory level in reproducing appropriate static dipole polarizabilities in a vacuum, we have shown that the procedure returns Henry's law constants consistent with the values experimentally observed in water and benzene at T = 25 °C and P = 1 bar for the first four elements of the series. The static dielectric constant (ε) of the investigated silicate melts and its optical counterpart (ε{sup ∞}) were then resolved through the application of a modified form of the Clausius-Mossotti relation. Argon has been adopted as a probe to depict its high-T solubility in melts through an appropriate choice of the solvent diameter σ{sub s}, along the guidelines already used in the past for simple media such as water or benzene. The σ{sub s} obtained was consistent with a simple functional form based on the molecular volume of the solvent. The solubility calculations were then extended to He, Ne, and Kr, whose dispersive and repulsive coefficients are available from theory and we have shown that their ab initio Henry's constants at high T reproduce the observed increase with the static polarizability of the series element with reasonable accuracy. At room temperature (T = 25 °C) the calculated Henry's constants of He, Ne, Ar, and Kr in the various silicate media predict higher solubilities than simple extrapolations (i.e., Arrhenius plots) based on high-T experiments and give rise to smooth trends not appreciably affected by the static polarizabilities of the solutes. The present investigation opens new perspectives on a wider application of PCM theory which can be extended to materials of great industrial interest at

  20. The solvation radius of silicate melts based on the solubility of noble gases and scaled particle theory

    NASA Astrophysics Data System (ADS)

    Ottonello, Giulio; Richet, Pascal

    2014-01-01

    The existing solubility data on noble gases in high-temperature silicate melts have been analyzed in terms of Scaling Particle Theory coupled with an ab initio assessment of the electronic, dispersive, and repulsive energy terms based on the Polarized Continuum Model (PCM). After a preliminary analysis of the role of the contracted Gaussian basis sets and theory level in reproducing appropriate static dipole polarizabilities in a vacuum, we have shown that the procedure returns Henry's law constants consistent with the values experimentally observed in water and benzene at T = 25 °C and P = 1 bar for the first four elements of the series. The static dielectric constant (ɛ) of the investigated silicate melts and its optical counterpart (ɛ∞) were then resolved through the application of a modified form of the Clausius-Mossotti relation. Argon has been adopted as a probe to depict its high-T solubility in melts through an appropriate choice of the solvent diameter σs, along the guidelines already used in the past for simple media such as water or benzene. The σs obtained was consistent with a simple functional form based on the molecular volume of the solvent. The solubility calculations were then extended to He, Ne, and Kr, whose dispersive and repulsive coefficients are available from theory and we have shown that their ab initio Henry's constants at high T reproduce the observed increase with the static polarizability of the series element with reasonable accuracy. At room temperature (T = 25 °C) the calculated Henry's constants of He, Ne, Ar, and Kr in the various silicate media predict higher solubilities than simple extrapolations (i.e., Arrhenius plots) based on high-T experiments and give rise to smooth trends not appreciably affected by the static polarizabilities of the solutes. The present investigation opens new perspectives on a wider application of PCM theory which can be extended to materials of great industrial interest at the core of

  1. Microscopic, Macroscopic, and Megascopic Melts: a simple model to synthesize simulation, spectroscopy, shock, and sink/float constraints on silicate melts and magma oceans

    NASA Astrophysics Data System (ADS)

    Asimow, P. D.; Thomas, C.; Wolf, A. S.

    2012-12-01

    Silicate melts are the essential agents of planetary differentiation and evolution. Their phase relations, element partitioning preferences, density, and transport properties determine the fates of heat and mass flow in the high-temperature interior of active planets. In the early Earth and in extrasolar super-Earth-mass terrestrial planets it is these properties at very high pressure (> 100 GPa) that control the evolution from possible magma oceans to solid-state convecting mantles. Yet these melts are complex, dynamic materials that present many challenges to experimental, theoretical, and computational understanding or prediction of their properties. There has been encouraging convergence among various approaches to understanding the structure and dynamics of silicate melts at multiple scales: nearest- and next-nearest neighbor structural information is derived from spectroscopic techniques such as high-resolution multinuclear NMR; first-principles molecular dynamics probe structure and dynamics at scales up to hundreds of atoms; Archimedean, ultrasonic, sink/float, and shock wave methods probe macroscopic properties (and occasionally dynamics); and deformation and diffusion experiments probe dynamics at macroscopic scale and various time scales. One challenge that remains to integrating all this information is a predictive model of silicate liquid structure that agrees with experiments and simulation both at microscopic and macroscopic scale. In addition to our efforts to collect macroscopic equation of state data using shock wave methods across ever-wider ranges of temperature, pressure, and composition space, we have introduced a simple model of coordination statistics around cations that can form the basis of a conceptual and predictive link across scales and methods. This idea is explored in this presentation specifically with regard to the temperature dependence of sound speed in ultramafic liquids. This is a highly uncertain quantity and yet it is key, in

  2. Seismic evidence for silicate melt atop the 410-km mantle discontinuity

    USGS Publications Warehouse

    Revenaugh, Justin; Sipkin, S.A.

    1994-01-01

    LABORATORY results demonstrating that basic to ultrabasic melts become denser than olivine-rich mantle at pressures above 6 GPa (refs 1-3) have important implications for basalt petrogenesis, mantle differentiation and the storage of volatiles deep in the Earth. A density cross-over between melt and solid in the extensively molten Archaean mantle has been inferred from komatiitic volcanism and major-element mass balances, but present-day evidence of dense melt below the seismic low-velocity zone is lacking. Here we present mantle shear-wave impedance profiles obtained from multiple-ScS reverberation mapping for corridors connecting western Pacific subduction zone earthquakes with digital seismograph stations in eastern China, imaging a ~5.8% impedance decrease roughly 330 km beneath the Sea of Japan, Yellow Sea and easternmost Asia. We propose that this represents the upper surface of a layer of negatively buoyant melt lying on top of the olivine ??? ??- phase transition (the 410-km seismic discontinuity). Volatile-rich fluids expelled from the partial melt zone as it freezes may migrate upwards, acting as metasomatic agents and perhaps as the deep 'proto-source' of kimberlites. The remaining, dense, crystalline fraction would then concentrate above 410 km, producing a garnet-rich layer that may flush into the transition zone.

  3. Partitioning of carbon between Fe-rich alloy melt and silicate melt in a magma ocean - Implications for the abundance and origin of volatiles in Earth, Mars, and the Moon

    NASA Astrophysics Data System (ADS)

    Chi, Han; Dasgupta, Rajdeep; Duncan, Megan S.; Shimizu, Nobumichi

    2014-08-01

    The budget and origin of carbon in Earth and other terrestrial planets are debated and one of the key unknowns is the fate of carbon during early planetary processes including accretion, core formation, and magma ocean (MO) crystallization. Here we determine, experimentally, the solubility of carbon in coexisting Fe-Ni alloy melt and basaltic silicate melt in shallow MO conditions, i.e., at 1-3 GPa, 1500-1800 °C. Oxygen fugacity of the experiments, estimated based on Fe (in metallic alloy melt)-FeO (in silicate melt) equilibrium, varied between ∼IW-0.4 and IW-1.0, where IW refers to the oxygen fugacity imposed by the coexistence of iron and wüstite. Four different starting mixes, each with 7:3 silicate:metal mass ratio and silicate melt NBO/T (estimated proportion of non-bridging oxygen with respect to tetrahedral cations; NBO/T=2×/total OT -4, where T = Si + Ti + Al + Cr + P) ranging from 0.81 to 1.54 were studied. Concentrations of carbon in the alloy melt were determined using electron microprobe whereas carbon contents of quenched basaltic glasses were determined using secondary ionization mass spectrometry (SIMS). Identification of carbon and hydrogen-bearing species in silicate glasses was performed using Raman and Fourier Transformed Infrared (FTIR) spectroscopy. Our results show that carbon in the metallic melt varies between 4.4 wt.% and 7.4 wt.% and increases with increasing temperature and modestly with increasing pressure but decreases with increasing Ni content of the alloy melt. Carbon concentration in the silicate melts, on the other hand, varies from 11 ± 1 ppm to 111 ± 7 ppm and is negatively correlated with pressure but positively correlated with temperature, the NBO/T, the oxygen fugacity and the water content of the silicate melts. Raman and FTIR results show that at our experimental conditions, carbon in silicate melt is dissolved both as hydrogenated species and CO32-. The calculated carbon partition coefficient DCmetal/silicate varies

  4. The effect of oxygen fugacity on the partitioning of nickel and cobalt between olivine, silicate melt, and metal

    NASA Technical Reports Server (NTRS)

    Ehlers, Karin; Grove, Timothy L.; Sisson, Thomas W.; Recca, Steven I.; Zervas, Deborah A.

    1992-01-01

    The effect of oxygen fugacity, f(O2), on the partitioning behavior of Ni and Co between olivine, silicate melt, and metal was investigated in the CaO-MgO-Al2O3-SiO2-FeO-Na2O system, an analogue of a chondrule composition from an ordinary chondrite. The conditions were 1350 C and 1 atm, with values of f(O2) varying between 10 exp -5.5 and 10 exp -12.6 atm (i.e., the f(O2) range relevant for crystal/liquid processes in terrestrial planets and meteorite parent bodies). Results of chemical analysis showed that the values of the Ni and Co partitioning coefficients begin to decrease at values of f(O2) that are about 3.9 log units below the nickel-nickel oxide and cobalt-cobalt oxide buffers, respectively, near the metal saturation for the chondrule analogue composition.

  5. Impact conditions required for formation of melt by jetting in silicates

    NASA Technical Reports Server (NTRS)

    Kieffer, S. W.

    1977-01-01

    It is demonstrated that the process of jetting which occurs when particles collide at oblique angles may produce melt at much lower velocities than are required for melt production in head-on collisions. The minimum velocities of impact required for jetting in aluminum, bronzitite, dunite, and quartz are calculated by the method of shock polars. The analysis, which depends on stated assumptions about attained pressures and the occurrence of jetting, uses shock-velocity particle-velocity equations of state with three shock regimes. The treatment indicates that jetting should arise in bronzitite, dunite, and quartz at relative velocities as low as 1-2 km/sec. At such velocities material which passes near the stagnation point in the jet-forming region is subjected to sufficiently high pressures so that it is probably melted.

  6. Multicomponent Diffusion between Felsic and Silicic Melts: Insights from Tektites and Experiments

    NASA Astrophysics Data System (ADS)

    Macris, C. A.; Asimow, P. D.; Zhang, Y.; Badro, J.; Stolper, E. M.; Eiler, J. M.

    2014-12-01

    Tektites (natural glasses formed as quenched impact melt ejecta) commonly contain inclusions of nearly pure silica glass ("lechatelierite") thought to be quenched from molten silica produced by melting of quartz grains. We investigated chemical diffusion between lechatelierite (~100% SiO2) and surrounding felsic glass (~73% SiO2) in a natural indochinite tektite and in experimental analogues. We discovered concentration profiles of major elements across lechatelierite-felsic glass contacts that reflect diffusion between the two melts at high T as the they followed a ballistic trajectory prior to quenching. The profiles provide information on multicomponent diffusion at the high-silica end of composition space and on the thermal histories of tektites. To reproduce the profiles, we undertook a series of high T melting experiments using an aerodynamic levitation laser furnace. A starting mixture of powdered natural tektite plus quartz grains was exposed to temperatures of 1800-2400˚C for 1-120 s. Direct comparison of concentration profiles between the indochinite and experiments reveals a best match at 2200˚C and 50 s. This experiment successfully reproduced all major aspects of the concentration profiles observed in the natural sample including diffusion length scale, asymmetry, order of steepness of major element profiles, and uphill diffusion of K2O. Not enough information is available to model the full multicomponent diffusion problem, but SiO2 and Al2O3 concentration profiles from lechatelierite to surrounding felsic glass in the experiments can be fit well as a diffusion couple between silica melt and adjacent felsic melt using an effective binary diffusion approach and assuming that the effective binary SiO2 and Al2O3 diffusivities depend exponentially on SiO2 concentration. Further quantification of the diffusion behavior should allow constraints on the thermal histories of tektites.

  7. Preparations of PbSe quantum dots in silicate glasses by a melt-annealing technique

    NASA Astrophysics Data System (ADS)

    Ma, D. W.; Cheng, C.; Zhang, Y. N.; Xu, Z. S.

    2014-11-01

    Silicate glass containing PbSe quantum dots (QDs) has important prospective applications in near infra-red optoelectronic devices. In this study, single-stage and double-stage heat-treatment methods were used respectively to prepare PbSe QDs in silicate glasses. Investigation results show that the double-stage heat-treatment is a favorable method to synthesize PbSe QDs with strong photoluminescence (PL) intensity and narrow full weight at half maximum (FWHM) in PL peak. Therefore, the method to prepare PbSe QDs was emphasized on the double-stage heat-treatment. Transmission electron microscopy measurements show that the standard deviations of the average QD sizes from the samples heat-treated at the development temperature of 550 °C fluctuate slightly in the range of 0.6-0.8 nm, while this deviation increases up to 1.2 nm for the sample with the development temperature of 600 °C. In addition, the linear relationship between the QD size and holding time indicates that the crystallization behavior of PbSe QDs in silicate glasses is interface-controlled growth in early stage of crystallization. The growth rates of PbSe QDs are determined to be 0.24 nm/h at 550 °C and 0.72 nm/h at 600 °C. In short, the double-stage heat-treatment at 450 °C for 20 h followed by heat-treatment at 550 °C for 5 h is a preferred process for the crystallization of PbSe QDs in silicate glass. Through this treatment, PbSe QDs with a narrow size dispersion of 5.0 ± 0.6 nm can be obtained, the PL peak from this sample is highest in intensity and narrowest in FWHM among all samples, and the peak is centered on 1575 nm, very close to the most common wavelength of 1550 nm in fiber-optic communication systems.

  8. Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

    NASA Astrophysics Data System (ADS)

    Panina, Liya; Stoppa, Francesco

    2009-12-01

    Melt inclusions in clinopyroxenes of olivine foidite bombs from Serra di Constantinopoli pyroclastic flows of the Vulture volcano (Southern Italy) were studied in detail. The rocks contain abundant zoned phenocrysts and xenocrysts of clinopyroxene, scarce grains of olivine, leucite, haüyne, glass with microlites of plagioclase and K-feldspar. The composition of clinopyroxene in xenocrysts (Cpx I), cores (Cpx II), and in rims (Cpx III) of phenocrysts differs in the content of Mg, Fe, Ti, and Al. All clinopyroxenes contain two types of primary inclusion-pure silicate and of silicate-carbonate-salt composition. This fact suggests that the phenomena of silicate-carbonate immiscibility took place prior to crystallization of clinopyroxene. Homogenization of pure silicate inclusions proceeded at 1 225 - 1 190°C. The composition of conserved melts corresponded to that of olivine foidite in Cpx I, to tephrite-phonolite in Cpx II, and phonolite-nepheline trachyte in Cpx III. The amount of water in them was no more than 0.9 wt.%. Silicate-carbonate inclusions decrepitated on heating. Salt globules contained salts of alkali-sulphate, alkali-carbonate, and Ca-carbonate composition somewhat enriched in Ba and Sr. This composition is typical of carbonatite melts when decomposed into immiscible fractions. The formation of sodalite-haüyne rocks from Vulture is related to the presence of carbonate-salt melts in magma chamber. The melts conserved in clinopyroxenes were enriched in incompatible elements, especially in Cpx III. High ratios of La, Nb, and Ta in melts on crystallization of Cpx I and Cpx II suggest the influence of a carbonatite melt as carbonatites have extremely high La/Nb and Nb/Ta and this is confirmed by the appearance of carbonatite melts in magma chamber. Some anomalies in the concentrations and relatives values of Eu and especially Ga seems typical of Italian carbonatite related melts. The mantle source for initial melts was, most likely, rather uniform

  9. Fluorine Partitioning between Nominally Anhydrous Minerals (cpx, ol, plag) and Silicate Melt

    NASA Astrophysics Data System (ADS)

    Guggino, S. N.; Hervig, R. L.

    2012-12-01

    Fluorine is a volatile constituent of magmas and hydrous mantle minerals, and the similar ionic radius of F- (1.33 Å) to that of OH- and O2- (1.40 Å) allows F- to substitute for OH- in hydrous phases and for oxygen in nominally anhydrous phases. Recent studies by Hervig and Bell (2005 Fall AGU), Guggino et al. (2007, 2009 Fall AGU), and Dalou et al. (2011) demonstrate that trace F, like H, is incorporated into nominally anhydrous minerals (NAMs) such as olivine (oliv), clinopyroxene (cpx), and plagioclase (plag), and the lower diffusivity of F compared to H in these phases renders F less subject to disturbance. Determining the behavior and controls of F incorporation into NAMs may provide a means to estimate the pre-eruptive F contents of degassed magmas and, by comparison, to better understand degassing behavior of H. In this study, we investigated the partitioning behavior of F in cpx, olivine, and plagioclase and examined the crystal-chemical controls and melt structural controls on F partitioning into olivine and cpx. Fluorine abundances were measured on phases (cpx, ol, plag, glass) from pre-existing experimental run products comprising olivine-minette (Esperanca and Holloway 1987), augite-minette (Righter and Carmichael 1996), basaltic andesite (Moore and Carmichael 1998) and latite (Esperanca and Holloway 1986) compositions. Fluorine ion intensities in the crystals and glass were measured by secondary ion mass spectrometry (SIMS) using a primary beam of 16O- ions and detection of negative secondary ions. Interfering 18OH- was separated from 19F- using high mass resolution. DFmin/melt varied with each melt composition and showed a progressive increase with increasing silica content of the melt such that oliv-minette < aug-minette < basaltic andesite < latite. For DFcpx/melt: oliv-minette (0.04-0.10); aug-minette (0.11-0.17); basaltic andesite (0.17-0.21); latite (0.12-0.27). For DFoliv/melt: oliv-minette (0.01-0.07); basaltic andesite (0.13-0.16). For

  10. Immiscible Transition from Carbonate-rich to Silicate-rich Melts in Eclogite+CO2 and Genesis of Ocean Island Melilitite

    NASA Astrophysics Data System (ADS)

    Dasgupta, R.; Stalker, K.; Hirschmann, M. M.

    2004-12-01

    Derivation of highly silica-undersaturated lavas such as olivine melilitites and melilite nephelinites from the mantle has been attributed to the effects of CO2. However, experimental studies have so far failed to demonstrate equilibrium of melilititic melts with a four-phase peridotite assemblage. Instead, the liquidus mineralogy of these silica-undersaturated magmas at high-pressures appears to be dominated by cpx1. Although, experimental partial melts from natural peridotite+CO2 span a continuum from carbonatite to alkali-basalts2, ocean-island melilitites have distinctly higher TiO2, FeO*, and CaO/(CaO+MgO)3,4 than compositions derived thus far from a carbonated lherzolite source. Partial melting experiments of a nominally anhydrous, natural eclogite with a small amount of added carbonate (SLEC1; 5 wt.% bulk CO2) were performed to investigate the transition between carbonate and silicate melts with increasing temperature. Experiments were conducted in a piston cylinder at 3 GPa from 1050 to 1400 ° C. Garnet and cpx appear in all the experiments and ilmenite is observed from 1075 to ˜1200 ° C. An Fe-bearing calcio-dolomitic melt is present from the solidus (1050-1075 ° C) up to 1375 ° C. Beginning at 1275 ° C, it coexists with a silica-poor silicate melt. Textural criteria indicate only a single CO2-rich silicate melt phase at 1400 ° C, coexisting with garnet and minor cpx. The liquidus temperature is estimated to be ˜1415 ° C from the melt fraction-temperature trend. With increasing temperature, the carbonate melt becomes richer in SiO2 ( ˜2 to 5 wt.%) and Al2O3 ( ˜0.75 to 2.25 wt.%) and poorer in CaO ( ˜30 to 25 wt.% from ˜1200 to 1375 ° C). Compositions of silicate partial melts change systematically with increasing temperature, increasing in SiO2 ( ˜36 to 41 wt.%), Al2O3 ( ˜4.5 to 9.5 wt.%), MgO ( ˜9.5 to 13 wt.%), CaO ( ˜8 to 14 wt.%) and decreasing in TiO2 ( ˜14 to 2.5 wt.%), FeO ( ˜20 to 13 wt.%), Na2O ( ˜3.3 to 1.7 wt.%). A wide

  11. Cerium oxidation state in silicate melts: Combined fO2, temperature and compositional effects

    NASA Astrophysics Data System (ADS)

    Smythe, Duane J.; Brenan, James M.

    2015-12-01

    To quantify the relative proportions of Ce3+ and Ce4+ in natural magmas, we have synthesized a series of Ce doped glasses ranging in composition from basalt to rhyolite (±H2O) at 0.001 and 1 GPa, under fO2 conditions varying from FMQ -4.0 to FMQ +8.4, and temperatures from 1200 to 1500 °C. The Ce4+/Ce3+ ratio in the experimental run products was determined both potentiometrically and in situ, using Ce M4,5-edge X-ray absorption near-edge structure (XANES) spectroscopy. For a given melt composition, the change in Ce4+/Ce3+ ratio with fO2 follows the trend predicted from the reaction stoichiometry assuming simple oxides as melt species. In addition to fO2, melt composition and water content have been found to be secondary controls on Ce4+/Ce3+, with more depolymerized melts and hydrous compositions favoring the stabilization of Ce3+. The Ce4+/Ce3+ ratio can be expressed through the equation,

  12. Silicate glasses and sulfide melts in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure, Virginia, USA

    USGS Publications Warehouse

    Belkin, H.E.; Horton, J.W., Jr.

    2009-01-01

    Optical and electron-beam petrography of melt-rich suevite and melt-rock clasts from selected samples from the Eyreville B core, Chesapeake Bay impact structure, reveal a variety of silicate glasses and coexisting sulfur-rich melts, now quenched to various sulfi de minerals (??iron). The glasses show a wide variety of textures, fl ow banding, compositions, devitrifi cation, and hydration states. Electron-microprobe analyses yield a compositional range of glasses from high SiO2 (>90 wt%) through a range of lower SiO2 (55-75 wt%) with no relationship to depth of sample. Some samples show spherical globules of different composition with sharp menisci, suggesting immiscibility at the time of quenching. Isotropic globules of higher interfacial tension glass (64 wt% SiO2) are in sharp contact with lower-surface-tension, high-silica glass (95 wt% SiO2). Immiscible glass-pair composition relationships show that the immiscibility is not stable and probably represents incomplete mixing. Devitrifi cation varies and some low-silica, high-iron glasses appear to have formed Fe-rich smectite; other glass compositions have formed rapid quench textures of corundum, orthopyroxene, clinopyroxene, magnetite, K-feldspar, plagioclase, chrome-spinel, and hercynite. Hydration (H2O by difference) varies from ~10 wt% to essentially anhydrous; high-SiO2 glasses tend to contain less H2O. Petrographic relationships show decomposition of pyrite and melting of pyrrhotite through the transformation series; pyrite? pyrrhotite? troilite??? iron. Spheres (~1 to ~50 ??m) of quenched immiscible sulfi de melt in silicate glass show a range of compositions and include phases such as pentlandite, chalcopyrite, Ni-As, monosulfi de solid solution, troilite, and rare Ni-Fe. Other sulfi de spheres contain small blebs of pure iron and exhibit a continuum with increasing iron content to spheres that consist of pure iron with small, remnant blebs of Fe-sulfi de. The Ni-rich sulfi de phases can be explained by

  13. Diffusion of major and trace elements in natural silicate melts as a tool to investigate timescales in magma mixing

    NASA Astrophysics Data System (ADS)

    González-García, Diego; Zezza, Angela; Behrens, Harald; Vetere, Francesco; Petrelli, Maurizio; Morgavi, Daniele; Perugini, Diego

    2016-04-01

    New melt injection into a shallow magma chamber is regarded as one of the potential triggers for explosive volcanic eruptions. Chemical diffusion occurring between the two mixing melts is a time-dependent process, and thus has the potential to shed light on the timescales involved in magma mixing events leading to an eruption. In order to achieve this, a complete database of diffusion coefficients in natural melts is a necessary prerequisite. We have carried out a set of 12 diffusion couple experiments in order to determine diffusion coefficients (D) of major and trace elements in two natural silicate melts. Two end-members from the Vulcano island (Aeolian archipelago, Italy) have been chosen for the experiments: a shoshonite (Vulcanello lava platform) and a rhyolitic obsidian (Pietre Cotte lava flow, La Fossa cone). Glasses from each end-member with added water contents of 0 wt%, 1 wt% and 2 wt% were produced in an Internally Heated Pressure Vessel (IHPV). Two glass cylinders with similar water content but different base composition are inserted in Au-Pd capsules and experiments are run in the IHPV at 1200° C with pressure from 0.5 to 3 kbar. Experiment capsules are rapidly quenched and analyzed by FTIR, EPMA and LA-ICP-MS for H2O, major and trace elements, respectively, along 2 mm linear profiles extending across the interface. A Boltzmann-Matano approach is used to obtain concentration-dependent diffusivities. The obtained concentration-distance profiles are asymmetric and extend deeper into the shoshonite relative to the rhyolite, indicating that diffusion is slower in the latter. Results show that diffusivities are notably accelerated by the presence of H2O in the melt. Experiments performed by using water-free glass show diffusivities one order of magnitude lower compared to glasses containing up to 2 wt% H2O. The effect of pressure, in the investigated range, is negligible and falls within measurement error. Among major elements, Si and Ti are the slowest

  14. Carbonatite-silicate immiscible melt inclusion in lamprophyre from Kutch, western India: Implication for plume-lithosphere interaction and initiation of Deccan Trap magmatism

    NASA Astrophysics Data System (ADS)

    Ray, Arijit; Paul, Dalim Kumar; Sen, Gautam; Biswas, Sanjib Kumar

    2014-05-01

    Kutch province of western India has undergone repeated rifting and marine transgression events from late Triassic to the late Cretaceous. Magmatic rocks occur in profusion in Kutch Basin. The southern part is characterized by occurrences of thick flows of tholeiitic basalt of Deccan Trap affinity, central part of Kutch Basin has numerous volcanic plugs of alkali basalt which is also considered as member of Deccan Trap, contain thin, discoidal mantle xenoliths of spinel lherzolite and wehrlite composition. Northern Kutch is dominated by suite of alkaline magmatic rocks similar to magmatic rocks of continental rift zone. The alkaline suite contains alkali pyroxenite, theralite, teschenite, basanite, nepheline syenite and kaersutite bearing lamprophyre (Ray et al., 2006, Das et al., 2007, Paul et al., 2008). The newly discovered east-west trending lamprophyre dyke swarm of northern Kutch (Pachham Island) is camptonite in composition and contains kaersutite phenocrysts in large proportion. These kaersutite phencrysts contain immscible melt/glass phases as melt inclusions. The lamprophyre yields an age of ca. 67 Ma.by Ar-Ar method (Sen et al., 2014 in press) synchronous with alkali basalt of central Kutch. The melt inclusions are fundamentally of two types - calciocarbonatite and alkaline silicate melts. We found sphene within carbonatitic melt and the rare mineral rhonite in silicate melt. Petrographic evidence indicates that carbonatite melt always occurs within alkali silicate melt as immiscible fraction. These carbonatite melts are extremely rich in CaCO3 (upto 95%) which contradicts the experimental results of carbonate melt composition (upto 80% CaCO3) in silicate-carbonate immiscible melt pair by Lee and Wyllie. The abundance of wehrlite xenoliths over lherzolite in alkali basalt, petrographic evidence of orthopyroxene to clinopyroxene transformation in wehrlite xenoliths, occurrence of calcite vein in mantle xenoliths indicate carbonatite metasomatism of spinel

  15. Evidence for a Phase Transition in Silicate Melt at Extreme Pressure and Temperature Conditions

    NASA Astrophysics Data System (ADS)

    Spaulding, D. K.; McWilliams, R. S.; Jeanloz, R.; Eggert, J. H.; Celliers, P. M.; Hicks, D. G.; Collins, G. W.; Smith, R. F.

    2012-02-01

    Laser-driven shock compression experiments reveal the presence of a phase transition in MgSiO3 over the pressure-temperature range 300-400 GPa and 10 000-16 000 K, with a positive Clapeyron slope and a volume change of ˜6.3 (±2.0) percent. The observations are most readily interpreted as an abrupt liquid-liquid transition in a silicate composition representative of terrestrial planetary mantles, implying potentially significant consequences for the thermal-chemical evolution of extrasolar planetary interiors. In addition, the present results extend the Hugoniot equation of state of MgSiO3 single crystal and glass to 950 GPa.

  16. Crystal-chemical controls on the partitioning of Sr and Ba between plagioclase feldspar, silicate melts, and hydrothermal solutions

    NASA Astrophysics Data System (ADS)

    Blundy, Jonathan D.; Wood, Bernard J.

    1991-01-01

    The isothermal (750°C) experiments of LAGACHE and DUJON (1987) reveal that the partitioning of Sr between plagioclase feldspar and hydrothermal solutions is a funtion of the anorthite (An) content of the plagioclase, indicating that crystal chemistry may exert a powerful influence on trace element partitioning. In order to compare these results with those on trace element partitioning between plagioclase and silicate melts we have compiled from the literature a large dataset of experimental and volcanic distribution coefficients ( D's) for Sr (and Ba). These data, which span a compositional range from lunar basalt to high silica rhyolite and a temperature range of over 650°C, show a relationship between DSr (and DBa) and mole fraction An ( XAn) which is similar to that exhibited by the hydrothermal results obtained at constant temperature. Plots of In DSr and In DBa versus XAn are linear with negative slope, indicating that both elements are more compatible in albite than anorthite. In terms of molar distribution coefficients ( D Sr∗) the hydrothermal and silicate melt data display an identical linear relationship between RT In D Sr∗ (where T is the absolute temperature in K and R is the gas constant, 8.314 JK -1 mol -1) and XAn. We conclude therefore that crystal chemistry provides the dominant control on partitioning of Sr and Ba into plagioclase and that the effects of temperature, pressure, and fluid composition are minor. Apparent relationships between DSr (and DBa) and the reciprocal temperature (1/ T) are artefacts of the linear relationships between XAn and 1/ T in the experimental studies. By defining a Henry's law standard state for the silicate melts and hydrothermal solutions, and considering plagioclases to be ternary regular solutions, we are able to relate the observed relationships between RT In D i∗ (where i is Ba or Sr) and XAn to the excess free energies of the trace element partitioning reactions between plagioclase and melt or

  17. Aluminum enrichment in silicate melts by fractional crystallization: some mineralogic and petrographic constraints.

    USGS Publications Warehouse

    Zen, E.

    1986-01-01

    The degree of Al saturation of an igneous rock may be given by its aluminium saturation index (ASI), defined as the molar ratio Al2O3/(CaO+K2O+Na2O). One suggested origin for mildly peraluminous granites (ASI 1-1.1) is fractional crystallization of subaluminous magmas (ASI 1. For hornblende to effectively cause a melt to evolve into a peraluminous composition, it must be able to coexist with peraluminous magmas; e.g. at = or <5 kbar hornblende can coexist with strongly peraluminous melts (ASI approx 1.5). Potentials and problems of using coarse-grained granitic rocks to prove courses of magmatic evolution are illustrated by a suite of samples from the Grayling Lake pluton, SW Montana. Such rocks generally contain a large cumulate component and should not be used as a primary test for the occurrence or efficacy of a fractionation process that might lead to peraluminous melts. The process is unlikely to give rise to peraluminous plutons of batholithic dimensions. A differential equation is presented which allows the direct use of mineral chemistry and modal abundance to predict the path of incremental evolution of a given magma.-R.A.H.

  18. Experimental determination of trace element partition coefficients between spinel and silicate melt: the influence of chemical composition and oxygen fugacity

    NASA Astrophysics Data System (ADS)

    Wijbrans, C. H.; Klemme, S.; Berndt, J.; Vollmer, C.

    2015-04-01

    We present new experimentally determined trace element partition coefficients between spinel and silicate melt. The experiments were performed at atmospheric pressure and at temperatures between 1220 and 1450 °C. To study the effect of redox conditions on trace element partitioning, we performed experiments under different redox conditions, with fO2 ranging from log -12 to log -0.7. The effect of different spinel compositions is also investigated. Our results show that spinel of all compositions readily incorporates the transition metals Ni, Co and Ga and the corresponding partition coefficients are >1. D Ni,Co,Ga are not significantly affected by changing melt composition, crystal composition or redox conditions. However, the multivalent trace elements V and Mo show a strong effect of redox conditions on their partitioning behavior with D V and D Mo highest at very reducing conditions and considerably lower at more oxidizing conditions. Partition coefficients for the high field strength elements Ti, Zr, Hf, Nb, and Ta and the elements Sc and Lu strongly depend on crystal composition, with D Ti and D Sc >1 for very Fe3+- or Cr-rich (and Al-poor) spinels, but one to two orders of magnitude lower in systems with Al-rich spinels. We present some examples on how our data may be used to reconstruct redox conditions of spinel formation. We also present some results on the partitioning of Pt and Rh between spinel and melt. D Rh depends strongly on redox conditions, while D Pt is not significantly affected.

  19. Mg-perovskite/silicate melt partition coefficients in the CMS system at 2430 C and 226 Kbars

    NASA Technical Reports Server (NTRS)

    Mcfarlane, Elisabeth A.; Drake, Michael J.; Gasparik, Tibor

    1992-01-01

    The partitioning of elements among lower mantle phases and silicate melts is of interest in unraveling the early thermal history of the Earth. Because of the technical difficulty in carrying out such measurements, only one direct set of measurements has been reported, and these results as well as interpretations based on them have generated controversy. The first set of direct measurements on a synthetic system in the CaO-MgO-SiO2 (CMS) is reported. An experiment was conducted at Stony Brook, using the USSA-2000 split sphere anvil apparatus. An experiment in the CMS system doped with oxides of Al, Ti, Sc, and Sm and run at a nominal temperature of 2380 C and pressure of 226 kbars is reported. Nominal temperatures were measured with a W 3 percent Re/W 25 percent Re thermocouple. The hot spot temperature, where the liquidus is located, is estimated to be at 2430 C. A 10 mm MgO octahedron was used in concert with 4 mm truncation edge lengths on the WC cubes. The sample was contained in a Re capsule which was inserted into a LaCrO3 furnace. Pressure was calibrated at 2000 C. Run duration was approximately 3 minutes. The charge was mounted in epoxy and analyzed using a CAMECA SX-50 electron microprobe. Standard operating conditions were employed, although counting time for the less abundant elements was increased to improved counting statistics. The melt is unquenchable, and forms a dendritic intergrowth of quench crystals and residual melt. It was analyzed using a 30 micron raster. The structural identity of the Mg-perovskite phase was confirmed using x ray microdiffractometry. The results of the investigation are presented.

  20. The stability of hibonite and other aluminous phases in silicate melts: Implications for the origin of hibonite-bearing inclusions

    NASA Technical Reports Server (NTRS)

    Beckett, J. R.; Stolper, E.

    1993-01-01

    Phase fields in which hibonite (Hib) and silicate melt coexist with spinel (Sp), CaAl4O7 (CA2), gehlenitic melilite (Mel), anorthite (An), or corundum (Cor) in the system CaO-MgO-Al203-SiO2-TiO2 (CMAST) were determined and activity models developed for Mel and Hib solid solutions. Experimentally determined partition coefficients for Ti between Hib and coexisting melt, D sub t, vary from 0.8 to 2.1 and generally decrease with increasing TiO2 content in the liquid (L). Based on Ti partioning between Hib and melt, bulk inclusion compositions and Hib-saturated liquid use phase diagrams, the Hib in Fluffy Type A inclusions (FTA's) from Allende and at least some of the Hib from Hib-rich inclusions is relict; much of the Hib from Hib-glass spherules probably crystallized from a melt under nonequilibrium conditions. Bulk compositions for all of these Ca-Al-rich inclusions (CAI's) are consistent with an origin as Mel + Hib + Sp + perovskite (Pv) proto-inclusions in which Mel was partially altered. In some cases, the proto-inclusion was partially or completely melted with vaporization occurring over a period of time sufficient to remove any Na introduced by the alteration process but frequently insufficient to dissolve all of the original hibonite. If equilibration temperatures based on Hib-bearing CAI's reflect condensation in a cooling gas of solar composition, then Hib + Cor condensed at approximately 1260 C (referenced to 10 exp -3 atm) and Hib + Sp + Mel at approximately 1215 +/- 10 C. Simple thermochemical models for the substitution of trace elements into the Ca-site of meteoritic Hib suggest that virtually all Eu is divalent in early condensate Hibs but that Eu(2+)/Eu(3+) decreases by a factor of 20 or more during the course of condensation, primarily because the ratio is proportional to the partial pressure of Al, which decreases dramatically as aluminous phases condense. The relative sizes of Eu and Yb anomalies in meteoritic Hibs and CAI's may be influenced by

  1. Melting of carbonated pelites at 2.5-5.0 GPa, silicate-carbonatite liquid immiscibility, and potassium-carbon metasomatism of the mantle

    NASA Astrophysics Data System (ADS)

    Thomsen, Tonny B.; Schmidt, Max W.

    2008-03-01

    Melting experiments on a Fe-rich carbonate-saturated pelite were performed at 850-1300 °C and 2.5-5.0 GPa to define melting relations, melt compositions, and the conditions under which carbonates remain residual. In the selected fertile bulk composition, 30 wt.% potassic granite (2.5 GPa) or phonolite (5.0 GPa) melt is generated at the fluid-absent solidus. The temperature of the latter increases from 900 °C at 2.4 GPa to 1070 °C at 5.0 GPa. Phengite + quartz/coesite control initial silicate melting and melt productivity through the reaction phengite + quartz/coesite +clinopyroxene + calcite = silicate melt + kyanite + garnet, which leaves most of the Fe-Mg-calcite in the residue. Na remains compatible in clinopyroxene (DNacpx/melt = 3.1 to 7.3 at the fluid-absent solidus), resulting in silicate melts with K2O/Na2O wt-ratios of 5.8-8.6. Such highly potassic carbonated silicate melts represent ideal metasomatic agents for the source mantle of group II kimberlites. From 3.7 to 5.0 GPa, Fe-Mg-calcite disappears only through the formation of Ca-carbonatite at 1100 °C. The experiments provide a possible source for Ca-carbonatites in combination with alkaline granitic to phonolitic melts at temperatures unlikely to be achieved during ongoing subduction. Large scale carbonate transfer to the subarc mantle can thus only be achieved when burying rates slow considerably down or subducted crust becomes incorporated into the mantle. Consequently, it is likely that carbonates will not be extensively mobilized in a typical subarc region, thus extending and confirming earlier results from subsolidus studies (Connolly, J.A.D., 2005. Computation of phase equilibria by linear programming: a tool for geodynamic modelling and its application to subduction zone decarbonation. Earth Planet. Sci. Lett. 236, 524-541.), that > 70-80% of the subducted carbonate will bypass the volcanic arc region and get buried to larger depths.

  2. Multi-technique equation of state for Fe2SiO4 melt and the density of Fe-bearing silicate melts from 0 to 161 GPa

    NASA Astrophysics Data System (ADS)

    Thomas, Claire W.; Liu, Qiong; Agee, Carl B.; Asimow, Paul D.; Lange, Rebecca A.

    2012-10-01

    We have conducted new equation of state measurements on liquid Fe2SiO4in a collaborative, multi-technique study. The liquid density (ρ), the bulk modulus (K), and its pressure derivative (K') were measured from 1 atm to 161 GPa using 1-atm double-bob Archimedean, multi-anvil sink/float, and shock wave techniques. Shock compression results on initially molten Fe2SiO4 (1573 K) fitted with previous work and the ultrasonically measured bulk sound speed (Co) in shock velocity (US)-particle velocity (up) space yields the Hugoniot: US = 1.58(0.03) up + 2.438(0.005) km/s. Sink/float results are in agreement with shock wave and ultrasonic data, consistent with an isothermal KT = 19.4 GPa and K' = 5.33 at 1500°C. Shock melting of initially solid Fe2SiO4 (300 K) confirms that the Grüneisen parameter (γ) of this liquid increases upon compression where γ = γo(ρo/ρ)q yields a qvalue of -1.45. Constraints on the liquid fayalite EOS permit the calculation of isentropes for silicate liquids of general composition in the multicomponent system CaO-MgO-Al2O3-SiO2-FeO at elevated temperatures and pressures. In our model a whole mantle magma ocean would first crystallize in the mid-lower mantle or at the base of the mantle were it composed of either peridotite or simplified "chondrite" liquid, respectively. In regards to the partial melt hypothesis to explain the occurrence and characteristics of ultra-low velocity zones, neither of these candidate liquids would be dense enough to remain at the core mantle boundary on geologic timescales, but our model defines a compositional range of liquids that would be gravitationally stable.

  3. Vapor pressure and vapor fractionation of silicate melts of tektite composition

    USGS Publications Warehouse

    Walter, Louis S.; Carron, M.K.

    1964-01-01

    The total vapor pressure of Philippine tektite melts of approximately 70 per cent silica has been determined at temperatures ranging from 1500 to 2100??C. This pressure is 190 ?? 40 mm Hg at 1500??C, 450 ?? 50 mm at 1800??C and 850 ?? 70 mm at 2100?? C. Determinations were made by visually observing the temperature at which bubbles began to form at a constant low ambient pressure. By varying the ambient pressure, a boiling point curve was constructed. This curve differs from the equilibrium vapor pressure curve due to surface tension effects. This difference was evaluated by determining the equilibrium bubble size in the melt and calculating the pressure due to surface tension, assuming the latter to be 380 dyn/cm. The relative volatility from tektite melts of the oxides of Na, K, Fe, Al and Si has been determined as a function of temperature, total pressure arid roughly, of oxygen fugacity. The volatility of SiO2 is decreased and that of Na2O and K2O is increased in an oxygen-poor environment. Preliminary results indicate that volatilization at 2100??C under atmospheric pressure caused little or no change in the percentage Na2O and K2O. The ratio Fe3 Fe2 of the tektite is increased in ambient air at a pressure of 9 ?? 10-4 mm Hg (= 106.5 atm O2, partial pressure) at 2000??C. This suggests that tektites were formed either at lower oxygen pressures or that they are a product of incomplete oxidation of parent material with a still lower ferricferrous ratio. ?? 1964.

  4. Trace element partitioning between ilmenite and anhydrous silicate melt: shedding light on the formation of lunar mare basalts

    NASA Astrophysics Data System (ADS)

    van Kan Parker, M.; Mason, P. R.; van Westrenen, W.

    2009-12-01

    Ilmenite (FeTiO3) is the main titanium-bearing, oxide mineral on the Moon. In contrast to its relatively minor role in terrestrial magmatic processes, it played a crucial role in the late stages of lunar magma ocean (LMO) crystallisation and in subsequent mare basalt formation. Quantifying its major and trace element incorporation behaviour at different conditions during partial melting and crystallisation processes is essential to constrain lunar interior evolution models. Trace element partitioning between ilmenite and silicate melt is poorly studied. Trace element partitioning between equilibrium phases depends on pressure, temperature, composition and oxygen fugacity. However, currently available ilmenite-melt partitioning data do not systematically consider these parameters. As a result, no predictive model explaining the large variations in partition coefficients seen in the literature is available. We performed systematic high-pressure, high-temperature ilmenite-melt partitioning experiments in the CaO-FeO-MgO-Al2O3-TiO2-SiO2 (CFMATS) system. Starting materials were doped with a wide range of trace elements (LILE, REE, HFSE and transition metals). Experiments were carried out at atmospheric pressure in platinum capsules, and at high pressure in an end-loaded piston cylinder at the VU University using graphite-lined Pt capsules. Major and trace element compositions of experimental charges were determined using a JEOL Electron Microprobe (VU University) and laser ablation ICP-MS (Utrecht University), respectively. Our results show that transition metals are generally compatible at pressures between 1.1 and 1.7 GPa and 1580 ± 10 K, with Cr having the highest partition coefficient (D ~ 6), followed by V (D ~ 3.5). Mn and Co have D values near 1. The HFSE are moderately incompatible at elevated pressures, with partition coefficients of 0.11-0.54. The REE are all incompatible, with HREE D values of 0.06 ± 0.03, and LILE D values are all <0.004. No clear pressure

  5. Ar diffusion in hydrous silicic melts: implications for volatile diffusion mechanisms and fractionation

    NASA Astrophysics Data System (ADS)

    Behrens, Harald; Zhang, Youxue

    2001-10-01

    The effect of dissolved water on the diffusivity of Ar in glasses and melts of rhyolitic and albitic compositions was investigated experimentally at pressures up to 1500 MPa and water contents of 0.1-5 wt%. The data for water-poor rhyolitic composition at 500 MPa can be described in the whole temperature range of 480-1102°C by a simple Arrhenius relationship DAr=2.14×10 -6 m 2/s exp(-18 883/ T). A 4.0 wt% increase in water content increases the Ar diffusivity by approximately one order of magnitude in both rhyolitic and albitic melts at 1000°C. In contrast to viscosity and total water diffusion, an exponential dependence of Ar diffusivity on water content was observed for the rhyolitic composition in the whole range of water contents. For water-poor rhyolite, Ar diffusivity depends on pressure with an apparent activation volume of 13-15 cm 3/mol at pressures up to 800 MPa. For water-rich rhyolite (˜5 wt% water), there is no significant pressure effect at 1000°C in the range 500-1500 MPa. Combining our data with previous data from Carroll [M.R. Carroll, Earth Planet. Sci. Lett. 103 (1991) 156-168], Ar diffusivity (in 10 -12 m 2/s) in rhyolitic melts can be expressed as: D Ar= exp[( 14.627- 17 913/T- 2.569P/T)+( 35 936/T+ 27.42P/T)X water] where T is in K, P in MPa, and Xwater is the mol fraction of water on a single oxygen basis. Except for two outlier points, error of estimates is ≤0.455 in terms of ln D for all data, covering a wide range of temperatures (480-1200°C), pressures (0.1-1500 MPa), and water contents (0.1-5 wt%). The new Ar diffusion data support the assumption that molecular H 2O diffusivity exponentially increases with water content [Y. Zhang, H. Behrens, Chem. Geol. 169 (2000) 243-262].

  6. Measuring the multicomponent diffusion matrix: Experimental design and data analysis for silicate melts

    SciTech Connect

    Trial, A.F.; Spera, F.J. )

    1994-09-01

    The extended form of Fick's Law, which allows the diffusive flux of a chemical species to be a function of all the concentration gradients, provides an accurate and useful description of chemical diffusion in isothermal, multicomponent systems. For an (N + 1)-component system, N[sup 2] diffusion coefficients are required, however. Although recent attempts to measure the multicomponent diffusion matrix for natural silicate compositions and simpler analogs have been unsuccessful, this does not mean that the extended Fick's Law is inapplicable. The authors show that the diffusion matrix cannot be measured unless the experiment is carefully designed. The optimal experiment is a set of 2N isothermal interdiffusion runs using at least N distinct diffusion couples. The concept of orthogonal couples, i.e., mutually perpendicular composition directions, provides a practical guide for choosing distinct couples. The number of couples required depends on the size of the errors in the concentration measurements. Chi-square fitting is an appropriate technique for analyzing diffusion data, because it allows one to directly apply thermodynamic constraints on the eigenvalues of the diffusion matrix. They discuss the details of implementing chi-square fitting for isothermal interdiffusion experiments, including Jacobian and Hessian matrices for both the finite and infinite diffusion couple models. They also apply this method to data from the literature, extracting the diffusion matrix for a Na[sub 2]O-CaO-SiO[sub 2] composition and making preliminary observations about some dacite-rhyolite and CaMgSi[sub 2]O[sub 6]-CaAl[sub 2]Si[sub 2]O[sub 8] experiments.

  7. Chromite-rich mafic silicate chondrules in ordinary chondrites: Formation by impact melting

    NASA Technical Reports Server (NTRS)

    Krot, Alexander N.; Rubin, Alan E.

    1993-01-01

    Chromium-rich chondrules constitute less than 0.1 percent of all ordinary chondrite (OC) chondrules and comprise three groups: chromian-spinel chondrules, chromian-spinel inclusions, and chromite-rich mafic silicate (CRMS) chondrules. Chromian-spinel chondrules (typically 100-300 microns in apparent diameter) exhibit granular, porphyritic and unusual textures and occur mainly in H chondrites. Their morphologies are distinct from the irregularly shaped chromian-spinel inclusions of similar mineralogy. Chromian-spinel chondrules and inclusions consist of grains of chromian-spinel embedded in plagioclase (Pl) or mesostasis of Pl composition. Many also contain accessory ilmenite (Ilm), high-Ca pyroxene (Px), merrillite (Mer), and rare olivine (Ol); some exhibit concentric mineral and chemical zoning. CRMS chondrules (300-1100 microns in apparent diameter) are generally larger than chromian-spinel chondrules and occur in all metamorphosed OC groups. Most CRMS chondrules are nearly spherical although a few are ellipsoidal with a/b aspect ratios ranging up to 1.7. Textures include cryptocrystalline, granular, radial, barred, and porphyritic varieties; some contain apparently relict grains. The chondrules consist of chromite (Chr), Ol and Pl, along with accessory Mer, troilite (Tr), metallic Fe-Ni (Met), Px and Ilm. The mesostasis in CRMS chondrules is nearly opaque in transmitted light; thus, they can be easily recognized in the optical microscope. Based on the similarity of mineralogy and chemistry between CRMS chondrules of different textures (opaque chromite-rich mesostasis, skeletal morphology of Ol grains, similar bulk compositions) we suggest that these chondrules form a genetically related population.

  8. The role of Al3+ on rheology and structural changes in sodium silicate and aluminosilicate glasses and melts

    NASA Astrophysics Data System (ADS)

    Le Losq, Charles; Neuville, Daniel R.; Florian, Pierre; Henderson, Grant S.; Massiot, Dominique

    2014-02-01

    Because of their importance in both the geosciences and the glass-making industry, alkali aluminosilicate melts have been the focal point of many past studies, but despite progress many problems remain unresolved, such as the complex behaviour of the thermodynamic properties of aluminium-rich alkali silicate melts. This paper presents a study of Na2O-Al2O3-SiO2 glasses and melts, containing 75 mol% SiO2 and different Al/(Al + Na) ratios. Their structure has been investigated by using Raman spectroscopy, as well as, 23Na, 27Al and 29Si 1D MAS NMR spectroscopy. Results confirm the role change of Na+ cations from network modifier to charge compensator in the presence of Al3+ ions. In addition, polymerization increases with increase of the Al/(Al + Na) ratio. These structural changes explain the observed variations in the viscosity of these melts. The viscosity data in turn allow us to calculate the configurational entropy of melts at the glass transition temperature [the Sconf(Tg)]. The variations of the Sconf(Tg) are strongly nonlinear, with sharp increases and decreases depending on the Al/(Al + Na) ratio. More importantly, a strong increase of the Sconf(Tg) is observed when a few Al2O3 is added to sodium silicate melt. A strong decrease is observed after crossing the tectosilicate join, when Al/(Al + Na) > 0.5 and when Al3+ ions are present in fivefold coordination, Al[5], in the glass. Furthermore, in situ27Al NMR spectra of the peraluminous melt show a clear increase of the Al[5] concentration with increasing temperature. When considered in combination with melt fragility and heat capacity, our data demonstrate that Al[5] is clearly a transient unit at high temperature in highly polymerized tectosilicate and peraluminous melts. However, when present in glasses, Al[5] increases the stability of the aluminosilicate network, hence the Tg of glasses. This could be explained by the ability of Al[5] to carry threefold coordinated oxygen atoms in its first coordination

  9. Temperature-dependent thermal expansivities of silicate melts: The system anorthite-diopside

    SciTech Connect

    Knoche, R.; Dingwell, D.B.; Webb, S.L. )

    1992-02-01

    The temperature-dependent thermal expansivities of melts along the join anorthite-diopside have been determined on glassy and liquid samples using a combination of calorimetry, dilatometry, and Pt double bob Archimedean densitometry. Supercooled liquid volumes and molar thermal expansivities were determined using scanning calorimetric and dilatometric measurements of properties in the glass region and their behavior at the glass transition. The extraction of low-temperature liquid molar expansivities from dilatometry/calorimetry is based on an assumed equivalence of the relaxation of volume and enthalpy at the glass transition using a method developed and tested by Webb et al. (1992). This method corrects for transient effects at the glass transition which can lead to serious overestimates of liquid thermal expansivity from peak' values. Superliquidus volumes were determined using double Pt bob Archimedean densitometry at temperatures up to 1,650C. The resulting data for liquid volumes near glass transition temperatures (810-920C) and at superliquidus temperatures (1,400-1,650C) are combined to yield thermal expansivities over the entire supercooled and stable liquid range. The molar expansivities are, in general, temperature dependent. The temperature-dependence of thermal expansivity increases from anorthite to diopside composition. The thermal expansivity of anorthite is essentially temperature independent, whereas that of diopside decreases by {congruent} 50% between 800 and 1,500C, with the consequence that the thermal expansivities of the liquids in the anorthite-diopside system converge at high temperature.

  10. Iron metal production in silicate melts through the direct reduction of Fe/II/ by Ti/III/, Cr/II/, and Eu/II/. [in lunar basalts

    NASA Technical Reports Server (NTRS)

    Schreiber, H. D.; Balazs, G. B.; Shaffer, A. P.; Jamison, P. L.

    1982-01-01

    The production of metallic iron in silicate melts by chemical reactions of Ti(3+), Cr(2+), and Eu(2+) with Fe(2+) is demonstrated under experimental conditions in a simplified basaltic liquid. These reactions form a basis for interpreting the role of isochemical valency exchange models in explanations for the reduced nature of lunar basalts. The redox couples are individually investigated in the silicate melt to ascertain reference redox ratios that are independent of mutual interactions. These studies also provide calibrations of spectral absorptions of the Fe(2+) and Ti(2+) species in these glasses. Subsequent spectrophotometric analyses of Fe(2+) and Ti(2+) in glasses doped with both iron and titanium and of Fe(2+) in glasses doped with either iron and chromium or iron and europium ascertain the degree of mutual interactions in these dual-doped glasses.

  11. Hydrothermal Fluids, Nebular Vapors and Silicate MELTS As Seem through the Eyes of Minerals

    NASA Astrophysics Data System (ADS)

    Sack, R. O.

    2014-12-01

    Three cases where advances in mineral thermochemistry provide new insights into geological processes are discussed: (I) Sb-rich fahlores are used to constrain compositions of hydrothermal fluids and processes responsible for Ag-Pb-Zn sulfide ores from three Ag mining districts, Keno Hill, (Yukon, Canada); Julcani, (Angaraes, Peru); Coeur d'Alene, (Idaho, USA), confirming that the Ag initially contained in galena solid solutions was a substantial contributor to the total Ag mined in each of them; (II) Al8/3O4-rich MgAl2O4-Al8/3O4 spinels may have condensed from the primordial solar nebula, with their Al8/3O4 annealed out with cooling, as AgSbS2 is "annealed" out of galena in Ag-Pb-Zn ore deposits. Such spinels may explain inconsistencies between mineral condensation sequences recorded in Ca-Al-rich inclusions (CAIs) in carbonaceous chondrites and those calculated assuming spinel was MgAl2O4. A new thermodynamical model and corundum-bearing CAIs, suggest we may anticipate realization of higher temperatures and pressures of canonical condensation than currently in vogue; (III) Fassitic pyroxenes in the composition space CaMgSi2O6 (Di) - CaTiAlSiO6 (Gr) - CaTi1/2Mg1/2AlSiO6 (AlBf) - CaAl2SiO6 (CATS) exhibit at least one prominent gap evident in composition data from CAIs. This may be interpreted as due to the near superposition of the extension of the Di- AlBf gap into this fassaite tetrahedron, with an isolated two-phase region formed by the double intersections of the (Gr+CATS) - AlBf critical curve with the surfaces of constant Ti(Al)-1 exchange potential characteristic of CAIs. A thermodynamic model for fassaites may provide context for critical thinking about CAI petrogenesis, as well as presaging potential refinements to the thermochemical model for pyroxenes in MELTS.

  12. The role of Al3+ on rheology and structural changes in sodium silicate and aluminosilicate glasses and melts

    NASA Astrophysics Data System (ADS)

    Le Losq, Charles; Neuville, Daniel R.; Florian, Pierre; Henderson, Grant S.; Massiot, Dominique

    2014-02-01

    Because of their importance in both the geosciences and the glass-making industry, alkali aluminosilicate melts have been the focal point of many past studies, but despite progress many problems remain unresolved, such as the complex behaviour of the thermodynamic properties of aluminium-rich alkali silicate melts. This paper presents a study of Na2O-Al2O3-SiO2 glasses and melts, containing 75 mol% SiO2 and different Al/(Al + Na) ratios. Their structure has been investigated by using Raman spectroscopy, as well as, 23Na, 27Al and 29Si 1D MAS NMR spectroscopy. Results confirm the role change of Na+ cations from network modifier to charge compensator in the presence of Al3+ ions. In addition, polymerization increases with increase of the Al/(Al + Na) ratio. These structural changes explain the observed variations in the viscosity of these melts. The viscosity data in turn allow us to calculate the configurational entropy of melts at the glass transition temperature [the Sconf(Tg)]. The variations of the Sconf(Tg) are strongly nonlinear, with sharp increases and decreases depending on the Al/(Al + Na) ratio. More importantly, a strong increase of the Sconf(Tg) is observed when a few Al2O3 is added to sodium silicate melt. A strong decrease is observed after crossing the tectosilicate join, when Al/(Al + Na) > 0.5 and when Al3+ ions are present in fivefold coordination, Al[5], in the glass. Furthermore, in situ27Al NMR spectra of the peraluminous melt show a clear increase of the Al[5] concentration with increasing temperature. When considered in combination with melt fragility and heat capacity, our data demonstrate that Al[5] is clearly a transient unit at high temperature in highly polymerized tectosilicate and peraluminous melts. However, when present in glasses, Al[5] increases the stability of the aluminosilicate network, hence the Tg of glasses. This could be explained by the ability of Al[5] to carry threefold coordinated oxygen atoms in its first coordination

  13. Joint-modeling of the Viscosity and the Electrical Conductivity of Silicate and Carbonatitic Melts and Implications for Geophysical Data Interpretation

    NASA Astrophysics Data System (ADS)

    Pommier, A.; Evans, R. L.; Key, K. W.

    2011-12-01

    We present an investigation of the relation between electrical conductivity (σ) and viscosity (η) of natural melts and its consequences for geophysical data interpretation. Both physicochemical properties are melt structure dependent and are very sensitive to even small changes in temperature and melt composition, including water content. Although many models have been developed for viscosity and for conductivity, attempts to combine both properties are scarce, particularly for complex natural systems. The interpretation of geophysical data can only be as good as our understanding of how physical properties such as conductivity and viscosity vary in the Earth's crust and mantle. Our conductivity-viscosity model is based on the optical basicity of silicate and carbonatitic compositions that count up to 10 oxides. From a structural point of view, the difference between viscosity and conductivity of melts lies in the fact that viscosity is mostly controlled by big network former anions (e.g. SiO44-) and conductivity by the mobility of smaller network modifier cations (e.g. Na+). By classifying each oxide as acidic, basic or amphoteric, optical basicity calculations of melt take into account the influence of forming and modifying species in the melt structure. This modeling approach is supported by recent findings showing that the optical basicity (Λ) of simple synthetic melts (CAS, CMAS systems) can be used to relate conductivity and viscosity [1]. Our model successfully reproduces experimental viscosity and electrical data from the literature over the temperature (T) range [800, 1400°C] by two simple semi-empirical equations in the form σ = f(log η, Λ, 1/T), with R2>0.84 for silicate melts and R2=0.98 for carbonatitic melts. At the scale of the field, the viscosity-conductivity model allows interpretation of conductive anomalies detected through electromagnetic soundings in terms of viscosity. Applications of this model will be presented for specific locations

  14. H2O-rich melt inclusions in fayalitic olivine from Hekla volcano: Implications for phase relationships in silicic systems and driving forces of explosive volcanism on Iceland

    NASA Astrophysics Data System (ADS)

    Portnyagin, Maxim; Hoernle, Kaj; Storm, Sonja; Mironov, Nikita; van den Bogaard, Christel; Botcharnikov, Roman

    2012-12-01

    Silicic Icelandic magmas are widely believed to contain low to moderate H2O content prior to degassing, and that their high explosivity mostly results from the interaction of the magmas with ice or meteoric water. Here we report the compositions of glass inclusions (SiO2=57-72 wt%, K2O=1.3-2.6 wt%) in Fe-rich olivines (Fo2-42) from the largest Holocene eruptions of Hekla volcano (H3 and H4) on Iceland, which preserved quenched melts with very high primary H2O contents (3.3-6.2 wt%). The silicic Hekla melts originate primarily by extensive (˜90%) crystal fractionation of H2O-poor (˜0.6 wt%) basalts and represent an end member in the systematics of terrestrial magmas because they originate at low fO2 (ΔQFM ˜-0.1 to -0.4) and have as high H2O contents as significantly more oxidized island-arc magmas (ΔQFM≥1). This demonstrates that H2O and ΔQFM do not correlate in silicic magmas from different tectonic settings, and that fO2, not H2O content, shows a major difference between silicic ocean-island (e.g., Icelandic) and island-arc magmas. Analysis of available experimental data suggests that high H2O activity and low fO2 expand the field of olivine stability in silicic melts. Low fO2 and low MgO content could also suppress crystallization of amphibole. On the basis of these results we propose that an anhydrous mineral assemblage bearing Fe-rich olivine in evolved volcanic and Skaergaard-type intrusive rocks does not imply low H2O in magmas prior to degassing but, in contrast to the commonly held view, is an indicator of H2O-rich silicic parental magmas crystallized at low fO2. Finally, the high H2O content in magma was a major driving force of the largest explosive eruptions of Hekla volcano and must be at least as important for driving silicic explosive volcanism on Iceland as magma-ice interaction.

  15. Light element partitioning between silicate and metallic melts: Insights into the formation and composition of Earth's core

    NASA Astrophysics Data System (ADS)

    Myhill, R.; Rubie, D. C.; Frost, D. J.

    2015-12-01

    The mass deficit of the Earth's core, and the increasing solubility of light elements into metallic iron with increasing pressure demonstrate that the Earth's core must contain several weight percent of light elements such as Si, O, C and S. These light elements place important constraints on the depth of the primordial magma ocean(s), the chemical potentials of many of these elements in coexisting phases during differentiation, the temperature of the inner core boundary, and the composition of the bulk Earth. The P-wave velocity, Earth's mass deficit, and depth of the inner core boundary place two important constraints on the chemical composition of the core, but there are multiple trade-offs which cannot be resolved using seismology alone. In this study, we use a large experimental partitioning dataset to build activity-composition models for light elements in metallic melts in equilibrium with oxide and silicate phases (both solid and liquid). We avoid the use of epsilon models, which commonly fail at solute concentrations above a few weight percent. Instead we employ a modified subregular solution model, using intermediate species to calculate excess free energies of mixing. Flexible models like these are required to fit the experimental data which spans 0 - 100 GPa and 1500 - 5500 K. Several heuristics are used to reduce the number of free parameters where they are not independently constrained. We use our models to investigate the conditions of core formation and the chemical composition of the Earth's core using the approach of Rubie et al. (2015; Icarus v.248; pp 89-108).

  16. Structural properties of sodium-rich carbonate-silicate melts: An in-situ high-pressure EXAFS study on Y and Sr

    NASA Astrophysics Data System (ADS)

    Pohlenz, J.; Pascarelli, S.; Mathon, O.; Belin, S.; Shiryaev, A.; Safonov, O.; Veligzhanin, A.; Murzin, V.; Irifune, T.; Wilke, M.

    2016-05-01

    In-situ EXAFS combined with a Paris-Edinburgh press (PEP) is an outstanding tool to investigate the local environment of trace elements in melts at high pressure and temperature. A novel design of the pressure assembly ensures a highly stable experimental setup (reaching temperatures of up to 2000 K at 2.5 GPa) while permitting the necessary level of X- ray transmission. This study focuses on the structural incorporation of the geochemically important trace elements Y and Sr in sodium-rich silicate-carbonate melts. Y and Sr K edge EXAFS were collected in transmission mode of the melt (at ∼2.5 GPa, 1600 K) and its respective quench products. Distinct changes in the XANES region suggest a change in site symmetry during the cooling process.

  17. Cumulate Fragments in Silicic Ignimbrites

    NASA Astrophysics Data System (ADS)

    Bachmann, O.; Ellis, B. S.; Wolff, J.

    2014-12-01

    Increasingly, studies are concluding that silicic ignimbrites are the result of the amalgamation of multiple discrete magma batches. Yet the existence of discrete batches presents a conundrum for magma generation and storage; if silicic magma batches are not generated nearly in situ in the upper crust, they must traverse, and reside within, a thermally hostile environment with large temperature gradients, resulting in low survivability in their shallow magmatic hearths. The Snake River Plain (Idaho, USA) is a type example of this 'multi-batch' assembly with ignimbrites containing multiple populations of pyroxene crystals, glass shards, and crystal aggregates. The ubiquitous crystal aggregates hint at a mechanism to facilitate the existence of multiple, relatively small batches of rhyolite in the upper crust. These aggregates contain the same plagioclase, pyroxene, and oxide mineral compositions as single phenocrysts of the same minerals in their host rocks, but they have significantly less silicic bulk compositions and lack quartz and sanidine, which occur as single phenocrysts in the deposits. This implies significant crystallization followed by melt extraction from mushy reservoir margins. The extracted melt then continues to evolve (crystallizing sanidine and quartz) while the melt-depleted margins provide an increasingly rigid and refractory network segregating the crystal-poor batches of magma. The hot, refractory, margins insulate the crystal-poor lenses, allowing (1) extended residence in the upper crust, and (2) preservation of chemical heterogeneities among batches. In contrast, systems that produce cumulates richer in low-temperature phases (quartz, K-feldspars, and/or biotite) favour remelting upon recharge, leading to less segregation of eruptible melt pockets and the formation of gradationally zoned ignimbrites. The occurrence of similar crystal aggregates from a variety of magmatic lineages suggests the generality of this process.

  18. Metal-Silicate Segregation in Deforming Dunitic Rocks: Applications to Core Formation in Europa and Ganymede

    NASA Technical Reports Server (NTRS)

    Hustoft, J. W.; Kohlstedt, D. L.

    2004-01-01

    Core formation is an important event in the evolution of a planetary body, affecting both the geochemical and geophysical properties of the body. Metal-silicate segregation could have proceeded either by settling of liquid metal through a magma ocean or by percolation of liquid metal through a solid silicate mantle. Percolation of metallic melt had previously been excluded as a viable segregation mechanism because metallic melts do not form an interconnected network under hydrostatic conditions, except at high melt fraction (>5 vol%), due to the high dihedral angle between metals and silicates (>60 ). Without an interconnected network, porous flow of metallic melt is impossible, leaving the magma ocean scenario as the only mechanism to form the core. Moment-of-inertia measurements of Europa and Ganymede from the Galileo probe indicate that they are differentiated. This evidence suggests that a method for segregating metals and silicates at temperatures low enough to retain volatile compounds must exist. We have investigated the effect of deformation on the distribution of metallic melts in silicates. We have deformed samples of olivine + 5-9 vol% Fe-S to strains of 2.5 in simple shear and find that the metallic melt segregates into melt-rich planes oriented at 20 to the shear plane. These metallic melt-rich bands are similar in structure to the silicate melt-rich bands reported by Holtzman, indicating that deformation can interconnect isolated metallic melt pockets and allow porous flow of non-wetting melts. Such a core formation process could have occurred in the jovian satellites.

  19. Redox Reaction in Silicate Melts Monitored by ''Static'' In-Situ Fe K-Edge XANES up to 1180 deg. C

    SciTech Connect

    Wilke, Max; Partzsch, Georg M.; Welter, Edmund; Farges, Francois

    2007-02-02

    A new experimental setup to measure in-situ kinetics of redox reactions in silicate melts is presented. To study the progress of the Fe-redox reaction, the variation of the signal is recorded at an energy, where the difference between the spectra of the oxidized and reduced Fe in the melt is largest (''static XANES''). To control the redox conditions, the gas atmosphere could be changed between to types of gases using computer-controlled valves (N2:H2 and air, respectively). In this way, a number of reduction/oxidation cycles can be monitored in-situ and continuously. Applied at the Fe K-edge in molten silicates, we obtained a set of high quality data, which includes the very first steps of the redox reaction. An Avrami-type equation is used to investigate rate-controlling parameters for the iron oxidation/reduction kinetics for two melts (basaltic and Na trisilicate) for temperatures up to 1180 deg. C.

  20. The partial molar sound speed of TiO2 in sodium silicate melts: Evidence for an exceptionally compressible component

    NASA Astrophysics Data System (ADS)

    Liu, Q.; Ai, Y.; Lange, R. A.

    2005-12-01

    Longitudinal acoustic velocities were measured at one bar by an ultrasonic frequency sweep acoustic interferometer for ten Na2O-TiO2-SiO2 (NTS) liquids for which previous density and thermal expansion measurements were made (Liu and Lange, 2001). This previous study showed that the partial molar volume of the TiO2 component varied systematically with composition and reflected changes in the average coordination of Ti4+ from values of ~4.6 to ~5.4. Sound speed data were collected at frequencies of 4.5, 5, and 6 MHz between 1233 and 1896 K; in all cases, the sound speeds decrease with increasing temperature. Six of the liquids share a similar (~25 mol%) TiO2 concentration, so that the effect of varying Na:Si ratio on the partial molar sound speed of the TiO2 component can be evaluated. The results for these ten NTS liquids were combined with sound speed data on Na2O-SiO2 liquids from the literature to derive the partial molar sound speed of the TiO2 component in these liquids. The results show that, at 1573 K, it is inversely correlated with SiO2 concentration, from values as low as 571±56 m/s to those as high as 1235±54 m/s, a variation of more than 100%. Fitted values for the partial molar sound speeds of the SiO2 and Na2O components at 1573 K are constants at 2538±52 and 2713±52 m/s, respectively. When the sound speed data are combined with density data to calculate melt compressibility, the results show that the TiO2 component is 3-15 more compressible than either the Na2O or SiO2 component. The partial molar compressibility of the TiO2 component is also strongly correlated to its partial molar thermal expansivity. It is shown that the TiO2 component is most compressible and most expansive when the average Ti4+ coordination in these sodium silicate liquids is near five, which strongly suggests that the abundance of five-coordinated Ti4+ enhances topological mechanisms of both compression and thermal expansion.

  1. C-O-H ratios of silicate melt inclusions in basalts from the Galapagos Spreading Center near 95 degrees W: a laser decrepitation mass spectrometry study

    NASA Technical Reports Server (NTRS)

    Yonover, R. N.; Sinton, J. M.; Sommer, M. A.; Gibson, E. K.

    1989-01-01

    Volatile ratios (primarily of H2O and CO2) in individual silicate melt (glass) inclusions in minerals have been analyzed using laser volatilization and mass spectrometry. A Nd-glass laser was used to produce 50-micrometer diameter pits in silicate melt inclusions. Released volatiles were analyzed directly with a computer-controlled quadrupole mass spectrometer. The detection limits for CO2 and H2O were on the order of 3 x 10(-14) and 3 x 10(-13) moles, respectively. The reproducibility for CO2/H2O was better than +/- 9%. The total range of volatile ratios from vitreous silicate glass inclusions contained in a suite of Galapagos lavas were: 0.018 to 1.193 for CO2/H2O; 0.002 to 0.758 for CO/H2O; 0 to 0.454 for CH4/H2O; and 0 to 0.432 for Ar/H2O. The mean CO2/H2O from the propagating rift (0.245 +/- 0.068) silicate glass inclusions is significantly lower than that of the actively failing rift (0.641 +/- 0.241); this difference probably reflects different degrees of degassing during magmatic histories for the two regions. Relatively undifferentiated failing rift magmas must have relatively short crustal residence times prior to eruption and, therefore, have not undergone significant degassing of CO2, as would appear to be the case for the more highly fractionated propagating rift magmas. The laser-mass spectrometric system described herein has the ability to act as a point-source probing device that can differentiate between the various volatile sites in minerals and rocks (as well as synthetic materials) on a micrometer scale.

  2. Density and compressibility of the molten lunar picritic glasses: Implications for the roles of Ti and Fe in the structures of silicate melts

    NASA Astrophysics Data System (ADS)

    Vander Kaaden, Kathleen E.; Agee, Carl B.; McCubbin, Francis M.

    2015-01-01

    The density and compressibility of four synthetic molten lunar picritic glasses was investigated from 0 to 10 GPa and 1748 to 2473 K. The picritic glasses were collected from the lunar surface during the Apollo missions, and they are hypothesized to have rapidly quenched as glass beads during pyroclastic fire fountain eruptions. The specific melt compositions investigated in the present study are the Apollo 15 green glass Type C (A15C, TiO2 = 0.26 wt%), the Apollo 14 yellow glass (A14Y, TiO2 = 4.58 wt%), the Apollo 17 orange glass 74220-type (A17O TiO2 = 9.12 wt%), and the Apollo 14 black glass (A14B, TiO2 = 16.40 wt%). These glasses are reported to represent primary unfractionated melts, making them a prime candidate for experimental studies into lunar basalt density and compressibility during partial melting of the lunar mantle. Sink-float experiments were conducted on the synthetic molten lunar glass compositions using a piston-cylinder apparatus (P < 2 GPa) and a Walker-style multi-anvil device (P > 2.5 GPa) in order to bracket the density of the melts. New sink-float data are reported for A15C, A14Y, and A17O, which are combined with previously published density and compressibility data on A15C, A17O, and A14B. Although the Ti-rich liquids are highly compressible at lower pressures, they become nearly incompressible at much higher pressures when compared to the molten low-Ti glasses. Consequently, the melts with the most TiO2 (A14B) are the least dense at higher pressures, a reversal of what is seen at lower pressures. This change in density and compressibility is attributed to changes in coordination of Ti and Fe in the silicate melt structure. As Ti4+ abundances in the silicate melt increase, predominantly [IV]Ti4+ and [IV]Fe2+ change to [VI]Ti4+ and [VI]Fe2+ in the melt structure. All of the data from the present study were used to calculate a Birch-Murnaghan equation-of-state (BM-EOS) for each melt composition. The BM-EOS model for each composition was

  3. A model that helps explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems

    NASA Astrophysics Data System (ADS)

    Duffield, Wendell A.; Ruiz, Joaquin

    1998-12-01

    Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.

  4. Trace element partitioning between ilmenite, armalcolite and anhydrous silicate melt: Implications for the formation of lunar high-Ti mare basalts

    NASA Astrophysics Data System (ADS)

    van Kan Parker, Mirjam; Mason, Paul R. D.; van Westrenen, Wim

    2011-08-01

    We performed a series of experiments at high pressures and temperatures to determine the partitioning of a wide range of trace elements between ilmenite (Ilm), armalcolite (Arm) and anhydrous lunar silicate melt, to constrain geochemical models of the formation of titanium-rich melts in the Moon. Experiments were performed in graphite-lined platinum capsules at pressures and temperatures ranging from 1.1 to 2.3 GPa and 1300-1400 °C using a synthetic Ti-enriched Apollo 'black glass' composition in the CaO-FeO-MgO-Al 2O 3-TiO 2-SiO 2 system. Ilmenite-melt and armalcolite-melt partition coefficients ( D) show highly incompatible values for the rare earth elements (REE) with the light REE more incompatible compared to the heavy REE ( DLaIlm-melt 0.0020 ± 0.0010 to DLuIlm-melt 0.069 ± 0.010 for ilmenite; DLaArm-melt 0.0048 ± 0.0023 to DLuArm-melt 0.041 ± 0.008 for armalcolite). D values for the high field strength elements vary from highly incompatible for Th, U and to a lesser extent W (for ilmenite: DThIlm-melt 0.0013 ± 0.0008, DUIlm-melt 0.0035 ± 0.0015 and DWIlm-melt 0.039 ± 0.005, and for armalcolite DThArm-melt 0.008 ± 0.003, DUArm-melt 0.0048 ± 0.0022 and DWArm-melt 0.062 ± 0.03), to mildly incompatible for Nb, Ta, Zr, and Hf (e.g. DHfIlm-melt 0.28 ± 0.05 and : DHfArm-melt 0.76 ± 0.07). Both minerals fractionate the high field strength elements with DTa/ DNb and DHf/ DZr between 1.3 and 1.6 for ilmenite and 1.3 and 1.4 for armalcolite. Armalcolite is slightly more efficient at fractionating Hf from W during lunar magma ocean crystallisation, with DHf/DW = 12-13 compared to 6.7-7.5 for ilmenite. The transition metals vary from mildly incompatible to compatible, with the highest compatibilities for Cr in ilmenite ( D ˜ 7.5) and V in armalcolite ( D ˜ 8.1). D values show no clear variation with pressure in the small range covered. Crystal lattice strain modelling of D values for di-, tri- and tetravalent trace elements shows that in ilmenite, divalent

  5. Simulating the behavior of volatiles belonging to the C-O-H-S system in silicate melts under magmatic conditions with the software D-Compress

    NASA Astrophysics Data System (ADS)

    Burgisser, Alain; Alletti, Marina; Scaillet, Bruno

    2015-06-01

    Modeling magmatic degassing, or how the volatile distribution between gas and melt changes at pressure varies, is a complex task that involves a large number of thermodynamical relationships and that requires dedicated software. This article presents the software D-Compress, which computes the gas and melt volatile composition of five element sets in magmatic systems (O-H, S-O-H, C-S-O-H, C-S-O-H-Fe, and C-O-H). It has been calibrated so as to simulate the volatiles coexisting with three common types of silicate melts (basalt, phonolite, and rhyolite). Operational temperatures depend on melt composition and range from 790 to 1400 °C. A specificity of D-Compress is the calculation of volatile composition as pressure varies along a (de)compression path between atmospheric and 3000 bars. This software was prepared so as to maximize versatility by proposing different sets of input parameters. In particular, whenever new solubility laws on specific melt compositions are available, the model parameters can be easily tuned to run the code on that composition. Parameter gaps were minimized by including sets of chemical species for which calibration data were available over a wide range of pressure, temperature, and melt composition. A brief description of the model rationale is followed by the presentation of the software capabilities. Examples of use are then presented with outputs comparisons between D-Compress and other currently available thermodynamical models. The compiled software and the source code are available as electronic supplementary materials.

  6. Geochemical diversity of late-Archaean Mg-K-rich mafic magmas (sanukitoids) and its implication for metasomatic processes between silicate melts and mantle peridotite

    NASA Astrophysics Data System (ADS)

    Laurent, Oscar; Martin, Hervé; Moyen, Jean-François; Doucelance, Régis

    2013-04-01

    The oldest high-Mg and high-K mafic magmas identified on Earth are the so-called sanukitoids that emplaced during the late-Archaean (3.0-2.5 Ga) in almost all cratonic domains worldwide. A compilation of >200 mafic to intermediate sanukitoid samples (mostly monzodiorites, quartz-diorites and quartz-monzonites with SiO2 = 45-62 wt.%), reveals that they clearly define two groups on the basis of their geochemistry: (1) low-Ti sanukitoids display moderate Ti, Fe as well as HFSE and REE contents, but high Mg# (0.55-0.70) and elevated concentrations in transition elements (Ni, Cr); (2) high-Ti sanukitoids, by contrast, are much richer in Ti, Fe, HFSE and LREE, but show significantly lower Mg# (0.45-0.55) as well as Ni and Cr contents. We investigated the origin of both series using geochemical modeling based on Monte-Carlo numerical simulations. As pointed out by previous work on experimental and natural systems [e.g. 1-2], our modeling indicates that both low- and high-Ti sanukitoids derive from the interactions, at mantle levels, between peridotite and a silicate melt. On the other hand, we demonstrated that (1) critical differences between low- and high-Ti sanukitoids (e.g. Ni, Cr, HFSE, REE contents) primarily results from two distinct mechanisms of melt-peridotite interactions; while (2) the nature of the metasomatic agent (either derived from metabasalts or metasediments in the models) only accounts for second-order variations within each group (e.g. K contents, Ba/Sr, La/Yb ratios and Eu anomaly). Specifically, the composition of low-Ti sanukitoids is best explained by a "one-step" hybridation of silicate melt with mantle peridotite, and is in equilibrium with a residual solid made up of garnet, clino- and orthopyroxene. By contrast, high-Ti sanukitoids likely derive from a "two-step" process: firstly, the silicate melt is fully consumed by interactions with peridotite, giving rise to a metasomatic, orthopyroxene-, amphibole- and phlogopite-rich assemblage. In

  7. Silicate volcanism on Io

    NASA Technical Reports Server (NTRS)

    Carr, M. H.

    1986-01-01

    This paper is mainly concerned with the nature of volcanic eruptions on Io, taking into account questions regarding the presence of silicates or sulfur as principal component. Attention is given to the generation of silicate magma, the viscous dissipation in the melt zone, thermal anomalies at eruption sites, and Ionian volcanism. According to the information available about Io, it appears that its volcanism and hence its surface materials are dominantly silicic. Several percent of volatile materials such as sulfur, but also including sodium- and potassium-rich materials, may also be present. The volatile materials at the surface are continually vaporized and melted as a result of the high rates of silicate volcanism.

  8. Partitioning of lanthanides and Y between immiscible silicate and fluoride melts, fluorite and cryolite and the origin of the lanthanide tetrad effect in igneous rocks

    NASA Astrophysics Data System (ADS)

    Veksler, Ilya V.; Dorfman, Alexander M.; Kamenetsky, Maya; Dulski, Peter; Dingwell, Donald B.

    2005-06-01

    Some F-rich granitic rocks show anomalous, nonchondritic ratios of Y/Ho, extreme negative Eu anomalies, and unusual, discontinuous, segmented chondrite-normalised plots of rare earth elements (REE). The effects of F-rich fluids have been proposed as one of the explanations for the geochemical anomalies in the evolved granitic systems, as the stability of nonsilicate complexes of individual rare earths may affect the fluid-melt element partitioning. The lanthanide tetrad effect, related to different configurations of 4f-electron subshells of the lanthanide elements, is one of the factors affecting such complexing behaviour. We present the first experimental demonstration of the decoupling of Y and Ho, and the tetrad effect in the partitioning of rare earths between immiscible silicate and fluoride melts. Two types of experiments were performed: dry runs at atmospheric pressure in a high-temperature centrifuge at 1100 to 1200°C, and experiments with the addition of H 2O at 700 to 800°C and 100 MPa in rapid-quench cold-seal pressure vessels. Run products were analysed by electron microprobe (major components), solution-based inductively coupled plasma mass spectrometry (ICP-MS) (REE in the centrifuged runs), and laser ablation ICP-MS (REE and Li in the products of rapid-quench runs). All the dry centrifuge runs were performed at super-liquidus, two-phase conditions. In the experiments with water-bearing mixtures, minor amounts of aqueous vapour were present in addition to the melts. We found that lanthanides and Y concentrated strongly in the fluoride liquids, with two-melt partition coefficients reaching values as high as 100-220 in water-bearing compositions. In all the experimental samples, two-melt partition coefficients of lanthanides show subtle periodicity consistent with the tetrad effect, and the partition coefficient of Y is greater than that of Ho. One of the mixtures also produced abundant fluorite (CaF 2) and cryolite (Na 3AlF 6) crystals, which enabled

  9. Mineralogy of silicate inclusions of the Colomera IIE iron and crystallization of Cr-diopside and alkali feldspar from a partial melt

    NASA Astrophysics Data System (ADS)

    Takeda, Hiroshi; Hsu, Weibiao; Huss, Gary R.

    2003-06-01

    We studied the mineralogy, mineral chemistry, and compositions of 48 interior silicate inclusions and a large K-rich surface inclusion from the Colomera IIE iron meteorite. Common minerals in the interior silicate inclusions are Cr diopside and Na plagioclase (albite). They are often enclosed by or coexist with albitic glasses with excess silica and minor Fe-Mg components. This mineral assemblage is similar to the "andesitic" material found in the Caddo County IAB iron meteorite for which a partial melt origin has been proposed. The fairly uniform compositions of Cr diopside (Ca 44Mg 46Fe 10) and Na plagioclase (Or 2.5Ab 90.0An 7.5 to Or 3.5Ab 96.1An 0.4) in Colomera interior inclusions and the angular boundaries between minerals and metal suggest that diopside and plagioclase partially crystallized under near-equilibrium conditions from a common melt before emplacement into molten metal. The melt-crystal assemblage has been called "crystal mush." The bulk compositions of the individual composite inclusions form an array between the most diopside-rich inclusion and plagioclase. This is consistent only with a simple mechanical mixing relationship, not a magmatic evolution series. We propose a model in which partly molten metal and crystal mush were mixed together by impact on the IIE parent body. Other models involving impact melting of the chondritic source material followed by growth of diopside and plagioclase do not easily explain near equilibrium growth of diopside and Na plagioclase, followed by rapid cooling. In the K-rich surface inclusion, K feldspar, orthopyroxene, and olivine were found together with diopside for the first time. K feldspar (sanidine, Or 92.7Ab 7.2An 0.1 to Or 87.3Ab 11.0An 1.7) occurs in an irregular veinlike region in contact with large orthopyroxene crystals of nearly uniform composition (Ca 1.3Mg 80.5Fe 17.8 to Ca 3.1Mg 78.1Fe 18.9) and intruding into a relict olivine with deformed-oval shape. Silica and subrounded Cr diopside are

  10. The distribution of H2O between silicate melt and nominally anhydrous peridotite and the onset of hydrous melting in the deep upper mantle

    NASA Astrophysics Data System (ADS)

    Novella, Davide; Frost, Daniel J.; Hauri, Erik H.; Bureau, Helene; Raepsaet, Caroline; Roberge, Mathilde

    2014-08-01

    The partitioning of H2O between a mantle peridotite assemblage and low degree hydrous melt has been investigated at 6 GPa (corresponding to ∼180 km depth) at a temperature of 1400 °C. Peridotite mineral phases were analysed from 6 melting experiments performed in a natural chemical system. The experiments contained ∼80 wt% of a low degree hydrous melt that was obtained through a series of experiments where the melt composition was iteratively adjusted until saturation with the appropriate peridotite assemblage was achieved. The melt is fluid-undersaturated at the conditions of the experiment. Ion microprobe measurements of the mineral phases indicate olivine H2O concentrations of 434±61 ppm wt and average clinopyroxene (cpx) concentrations of 1268±173 ppm wt H2O. Orthopyroxene (opx) and garnet contain 700±46 ppm wt and 347±83 ppm wt H2O, respectively. The H2O content of the hydrous melts was determined by mass balance to be 11±0.5 wt% H2O. H2O partition coefficients between minerals and melt (DH2Omin/melt=XH2Omin/XH2Omelt) are 0.0040±0.0006 for olivine, 0.0064±0.0004 for opx, 0.0115±0.0016 for cpx and 0.0032±0.0008 for garnet. Using the determined H2O partition coefficients the onset and extent of melting at conditions equivalent to 180 km below mid-ocean ridges was determined as a function of mantle H2O content. Current estimates for the H2O content of the depleted mantle (50-200 ppm wt H2O) are insufficient to induce mantle melting at this depth, which requires ∼700 ppm wt H2O to produce 0.1% melting and 1600 ppm wt H2O for 1% melting, along an adiabat with a potential temperature of 1327 °C. Melting can occur at these conditions within the mantle source of ocean island basalts, which are estimated to contain up to 900 ppm wt H2O. If adiabatic temperatures are 200 °C higher within such plume related sources, then melt fractions of over 1% can be reached at 180 km depth. In addition, a model for the distribution of H2O between peridotite mineral

  11. Flux of carbonate melt from deeply subducted pelitic sediments: Geophysical and geochemical implications for the source of Central American volcanic arc

    NASA Astrophysics Data System (ADS)

    Tsuno, Kyusei; Dasgupta, Rajdeep; Danielson, Lisa; Righter, Kevin

    2012-08-01

    We determined the fluid-present and fluid-absent near-solidus melting of an Al-poor carbonated pelite at 3-7 GPa, to constrain the possible influence of sediment melt in subduction zones. Hydrous silicate melt is produced at the solidi at 3-4 GPa whereas Na-K-rich carbonatite is produced at the solidi at ≥5 GPa for both starting compositions. At ≥5 GPa and 1050°C, immiscible carbonate and silicate melts appear with carbonate melt forming isolated pockets embedded in silicate melt. Application of our data to Nicaraguan slab suggests that sediment melting may not occur at sub-arc depth (˜170 km) but carbonatite production can occur atop slab or by diapiric rise of carbonated-silicate mélange zone to the mantle wedge at ˜200-250 km depth. Flux of carbonatite to shallower arc-source can explain the geochemistry of Nicaraguan primary magma (low SiO2 and high CaO, Ba/La). Comparison of carbonate-silicate melt immiscibility field with mantle wedge thermal structure suggests that carbonatite might temporally be trapped in viscous silicate melt, and contribute to seismic low-velocity zone at deep mantle wedge of Nicaragua.

  12. Simplicity in Pressure-induced Structural Change in Multi-component Silicate Melts in Earth's Interiors: Insights from Multi-nuclear NMR and Multi-edge Inelastic X-ray Scattering

    NASA Astrophysics Data System (ADS)

    Lee, S.

    2011-12-01

    The chemical differentiation of the primary mantle was controlled by the properties of silicate melts at high pressure. These properties vary non-linearly with changes in pressure. Whereas the key to understanding these complex and non-linear changes in melt properties is the degree of melt-polymerization [e.g. non-bridging oxygen (NBO) fraction] at high pressure, the nature of changes in the melt structure at high pressures remains poorly constrained. While the NBO fraction at 1 atm is often regarded as a chemical constraint from which other properties of melt structure are predicted, the systematic relation between NBO fraction at high pressure and melt composition has not been available. The advances in multi-nuclear NMR and multi-edge inelastic x-ray scattering allow us to obtain details of the pressure-induced changes in the degree of melt polymerization and cation coordination number in multi-component melts up to 40 GPa (e.g. Lee Proc. Nat. Aca. Sci. 2011, 108, 6847; Sol. St. NMR. 2010, 38, 45; Lee et al. Phys. Rev. Lett. 2009, 103, 095501; Proc. Nat. Aca. Sci. 2008, 105, 7925). Here, we show that the fraction of highly coordinated Al in multi-component silicate melts at a given pressure vary nonlinearly with variations of NBO/T: [5,6]Al fraction at 8 GPa increases with decreasing degree of melt polymerization from ~8% for fully polymerized albite melt (NBO/T=0) to ~37% for partially depolymerized melt (NBO/T=0.29). Then it gradually decreases to ~15% with further increase in NBO/T of 0.67. This observed trend at a given pressure indicates competing densification mechanisms involving steric hindrance vs. changes of NBO fraction in the silicate melts. Furthermore, we also show that NBO fraction of silicate melts decreases slightly with increasing pressure at lower pressures but it abruptly increases with a further increase in pressure, regardless of composition. By introducing the transition pressure in which the NBO fraction is expected to be 50% of the

  13. A model that helps explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems

    USGS Publications Warehouse

    Duffield, W.A.; Ruiz, J.

    1998-01-01

    Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a

  14. Shock-Induced Melting of Martian Basalts: Insights on Subducting Oceanic Crust Melting Processes

    NASA Astrophysics Data System (ADS)

    Beck, P.; Gillet, P.; Barrat, J.-A.; Gautron, L.; Daniel, I.; El Goresy, A.

    2003-04-01

    Experiments carried out on rocks at upper and lower mantle P-T conditions have produced series of candidate minerals for the Earth mantle mineralogical model. Basaltic compositions can also suffer ultra high-pressure and temperature when subducting in the mantle. The phase diagram of basalts has been studied to characterize potential chemical and mineralogical heterogeneities produced by partial melting and phase transformations of the oceanic crust. Shergottites that represent the most important sub-class of Martian meteorite have compositions close to terrestrial basalts and gabbros. During their extraction from Mars, they were severely shocked with pressures up to 50 GPa. These shocks induced partial melting. These melt pocket are an opportunity to study melting phenomena of basaltic compositions (i.e. oceanic crust) under high-pressure. We have performed a Raman spectroscopy investigation to determine the mineralogy of the melt pockets. Four shergottites were studied, NWA 480, NWA 856, NWA 1068 and Zagami. In each meteorite, abundant "large" minerals in melt pockets are hollandite (both Ca-Na and K-Na hollandite), stishovite, amorphous pyroxene and high-pressure phosphate. Meltpocket matrix seems to have a similar mineralogy as "megacrysts". In NWA 856 we observed at a melt pocket rim that maskelynite successively transforms into hollandite, and a polycrystalline aggregate. This aggregate was identified as a mixture of stishovite and a calcium aluminosilicate phase (CAS), a phase previously described in high-pressure experiments, but never observed in natural samples. The Raman spectra identifies unambiguously this silicate of composition CaAl_4Si_2O11 and of Ba-ferrite type structure. Such a phase is supposed to be present in basalt subsolidus melting experiments for pressures above 25 GPa and temperatures between 2500 and 2700 K. Its discovery reinforces the proposition that this CAS phase is a valuable candidate for hosting Al in subducting oceanic crust.

  15. Redox controls on tungsten and uranium crystal/silicate melt partitioning and implications for the U/W and Th/W ratio of the lunar mantle

    NASA Astrophysics Data System (ADS)

    Fonseca, Raúl O. C.; Mallmann, Guilherme; Sprung, Peter; Sommer, Johanna E.; Heuser, Alexander; Speelmanns, Iris M.; Blanchard, Henrik

    2014-10-01

    The timing of core formation is essential for understanding the early differentiation history of the Earth and the Moon. Because Hf is lithophile and W is siderophile during metal-silicate segregation, the decay of 182Hf to 182W (half-life of 9 Ma) has proven to be a useful chronometer of core-mantle differentiation events. A key parameter for the interpretation of 182Hf/182W data is the Hf/W ratio of the primitive (i.e. undepleted) mantle. Since W is incompatible during mantle melting, its ratio relative to U and other similarly incompatible elements in basalts (e.g. Th, La) may be used as proxies for their mantle sources. However, the assumption that W and U are equally incompatible may be flawed for petrological systems that equilibrated over a large range of oxygen fugacity (fO2). Although W is typically perceived as being homovalent, evidence suggests that U is heterovalent over the range of fO2 inferred for the silicate mantles of the Earth and the Moon. Here we report new partitioning data for W, U, high-field-strength elements (HFSE), and Th between clinopyroxene, orthopyroxene, olivine, plagioclase and silicate melt. In agreement with previous studies, we show that these elements behave as homovalent elements at fO2 characteristic of Earth's upper mantle. However, both W and U become more compatible at low fO2, indicating a change in their redox state, with W becoming more compatible at progressively lower fO2. This result for W is particularly unexpected, because this element was thought to be hexavalent even at very low fO2. The much higher compatibility of W4+ (the species inferred here at low fO2) relative to W6+ means that even a small fraction of W4+ will have a significant effect on the overall compatibility of W. Our results imply that over the range of reducing conditions in which lunar differentiation is thought to have taken place (i.e. ∼IW-2 to IW-0.5), W is likely to become fractionated from U. When our partitioning data are applied to model

  16. A Tale of Two Melt Rocks: Equilibration and Metal/Sulfide-Silicate Segregation in the L7 Chondrites PAT 91501 and LEW 88663

    NASA Astrophysics Data System (ADS)

    Harvey, R. P.

    1993-07-01

    Type 7 ordinary chondrites have experienced temperatures near or beyond those necessary for partial melting. Two recently collected Antarctic specimens, PAT91501 (PAT) and LEW88663 (LEW), have been tentatively identified as L7 chondrites based on mineral and oxygen isotope compositions [1,2]. The petrology and mineralogy of these meteorites suggests that they have undergone significant metal/sulfide-silicate segregation, with implications for meteorite parent bodies. PAT consists of an equigranular contact-framework of nearly euhedral olivine grains, with interstitial spaces filled by plagioclase, pyroxenes, and several minor phases. Ortho- and clinopyroxene occur in an exsolution relationship. Olivine and pyroxene are highly equilibrated, varying <<1% in Fe-endmember content. Pyroxene equilibration temperatures calculated for PAT using the methods of [3] are self-consistent at about 1180 degrees C. In thin section, PAT contains only traces of metal, as tiny isolated blebs in sulfide grains; large (>1 cm) globular sulfide inclusions are seen in hand-sample [1], but are not present in the section examined. LEW was originally classified as an achondrite with olivine and pyroxene compositions similar to those in L chondrites [2]. Metal is absent in LEW, although the specimen is small and heavily rusted, making it impossible to gauge the original metal content. Olivine grains are commonly rounded in shape and seldom in contact with more than a few other grains. LEW olivine and pyroxene are also highly equilibrated. Veins of Ni-bearing metal oxides and sulfides are common. Both low- and high-Ca pyroxene occur as discrete grains, orthopyroxene often poikilitically enclosing olivine. Pyroxene equilibration temperatures for LEW are more variable than those for PAT and consistently lower, with an average around 900 degrees C. The various textural and compositional characteristics of PAT and LEW suggest they have experienced partial melting to varying degrees. Both visually

  17. (Energetics of silicate melts from thermal diffusion studies): Progress report for the second year's activities, January--December 1988

    SciTech Connect

    Lesher, C.; Walker, D.

    1988-01-01

    The second year of this three year renewal has been used to continue data collection and analysis of thermal (Soret) diffusion in silicate liquid and explore the related process of thermal migration in subliquidus magmas. During the past year we have expanded our experimental capabilities for thermal gradient work by the construction of two new miniaturized piston-cylinder devices capable of 20kb. This has greatly alleviated the bottleneck on our existing facilities and has permitted us to undertake long term thermal diffusion experiments which have been prohibitive in the past. Data collection efforts have also been materially aided by advances in thermal insulation in the pressure media outside our pressurized cylindrical heaters. BaCO/sub 3/ + 10%Cr/sub 2/O/sub 3/ is very effective in protecting the pressure vessel core from thermal deterioration with the result that the heater inside and outside diameters can be substantially increased. This permits several charges to be run simultaneously in an axisymmetric cluster around a double or triple junction thermocouple which can measure axial thermal gradients in situ. These thermal insulation and charge volume increase innovations also have been adapted in our on going studies of mineral-liquid element partitioning, silicate mineral dissolution and silicate liquid interdiffusion and should prove to be wide applicability and utility in other piston-cylinder laboratories, as well. 13 refs.

  18. The Friction Evolution of Siliceous Rocks during High-Velocity Slip By Thermal Activated Transition from Powder Lubrication and Rolling to Gouge Melting

    NASA Astrophysics Data System (ADS)

    Chen, X.; Madden, A. S.; Reches, Z.

    2014-12-01

    Experimental analyses of the frictional strength of siliceous rocks (granite, tonalite, and diorite) sheared in a rotary apparatus in the velocity range of 0.002-1 m/s (0.3-7.1 MPa, 0.002 - 1 m/s, total slip up to 60 m) revealed that: (1) During long slip-distances (tens of m) at low to moderate velocity (< 5 cm/s) the friction coefficient evolves with a weakening-strengthening-weakening path (Fig. 1a); and (2) The dependence of the friction coefficient on the slip-velocity is non-monotonous with weakening-strengthening-weakening sections (Fig. 1b) (Reches & Lockner, 2010). In a typical run with granite (Fig. 1a), the friction coefficient dropped from a static value of 0.86 to a steady value of 0.35 after 2.5 m of slip, followed by a sharp increase to 0.5±0.1 after ~7 m that was maintained for the next 10 m. Then, the friction started to increase again at 17 m to 0.78 at ~20 m, and finally dropped rapidly to 0.4. The first weakening stage (< 2.5m) is associated with formation of cohesive gouge flakes made of mixture of partially hydrated and recrystallized fine-grained gouge (20-50 nm). The top of these flakes displayed cylindrical rolls, 1 micron in diameter, oriented normal to slip, and the macroscopic weakening correlates with the presence of abundant rolls. SEM analysis of fault surfaces at the second weakening stage (> 17m) revealed abundant melt features such as stretched melt drops, melt coating of solid grains and abundant voids in the melt matrix, contrasting with the total melt in high velocity experiments. These friction-distance curves in our granite experiments (e.g., Fig. 1a) bears a similar path of gabbro friction curve at high velocity (Hirose and Shimamoto 2005). We propose that this non-monotonous friction evolution can be explained as a phase transition from initial pulverization of the brittle stage (low velocity, low normal stress, small slip distance), that leads to powder lubrication by powder rolling, to partial-to-full melting of the

  19. Partitioning of Ni, Co and V between Spinel-Structured Oxides and Silicate Melts: Importance of Spinel Composition

    NASA Technical Reports Server (NTRS)

    Righter, K.; Leeman, W. P.; Hervig, R. L.

    2006-01-01

    Partitioning of Ni, Co and V between Cr-rich spinels and basaltic melt has been studied experimentally between 1150 and 1325 C, and at controlled oxygen fugacity from the Co-CoO buffer to slightly above the hematite magnetite buffer. These new results, together with new Ni, Co and V analyses of experimental run products from Leeman [Leeman, W.P., 1974. Experimental determination of the partitioning of divalent cations between olivine and basaltic liquid, Pt. II. PhD thesis, Univ. Oregon, 231 - 337.], show that experimentally determined spinel melt partition coefficients (D) are dependent upon temperature (T), oxygen fugacity (fO2) and spinel composition. In particular, partition coefficients determined on doped systems are higher than those in natural (undoped) systems, perhaps due to changing activity coefficients over the composition range defined by the experimental data. Using our new results and published runs (n =85), we obtain a multilinear regression equation that predicts experimental D(V) values as a function of T, fO2, concentration of V in melt and spinel composition. This equation allows prediction of D(V) spinel/melt values for natural mafic liquids at relevant crystallization conditions. Similarly, D(Ni) and D(Co) values can be inferred from our experiments at redox conditions approaching the QFM buffer, temperatures of 1150 to 1250 C and spinel composition (early Cr-bearing and later Ti-magnetite) appropriate for basic magma differentiation. When coupled with major element modelling of liquid lines of descent, these values (D(Ni) sp/melt=10 and D(Co) sp/melt=5) closely reproduce the compositional variation observed in komatiite, mid-ocean ridge basalt (MORB), ocean island basalt (OIB) and basalt to rhyolite suites.

  20. The role of alkalis in the solubility of H2O and CO2in silicate melts

    NASA Astrophysics Data System (ADS)

    Vetere, F.; Behrens, H.; Botcharnikov, R. E.; Holtz, F.; Fanara, S.

    2013-12-01

    In order to investigate the role of alkalis on the behavior of H2O and CO2 in magmatic systems, the solubility of volatiles in phonotephritic melts was investigated experimentally and compared to other melt compositions. The investigated compositions have Na2O/K2O ratios (in wt %) of 0.26 (Ab1, natural phonotephrite from Alban Hills, Italy), 0.98 (Ab2) and 3.82 (Ab3). Experiments were run at 1250°C and 500 MPa in an internally heated gas pressure vessel. The mole fraction of water (XH2O) in the fluid phase composed of H2O and CO2 varied in the range from 0 to 1. For the calibration of carbon-related IR bands in glasses, the total carbon content of synthesized glass standards was measured by combustion and subsequent IR spectroscopy using an ELTRA CS800 analyzer. Karl Fischer Titration method was used to quantify the H2O content of the glasses. Absorption spectra were recorded in the mid-infrared (MIR) using a Bruker IFS88 FTIR spectrometer coupled with an IR-ScopeII microscope. CO2 is bounded in the investigated glasses as CO32- exclusively and its concentration was quantified by the peak height of the 1430 cm-1 band. A drastic change was observed in the absorption coefficients, ɛ, with values of 294 × 35, 329 × 40 and 244 × 23 L/(mol cm) , for Ab1, Ab2, and Ab3, respectively, so that the highest ɛ value is related to the Na-rich composition. There is no evident effect of the Na/K ratio on the concentrations of dissolved H2O and CO2 in the melts. The solubility of CO2 and H2O in those melts at 500 MPa is 0.95 wt % CO2 and 10.07 wt% H2O for XH2O of 0 and 1, respectively. Results are compared with the existing literature data and models and confirm the very high solubility of CO2 in phonotephritic melts [1]. Our experimental data indicate that the melt composition in terms of alkali contents influences significantly the extinction coefficient values for CO2 and that appropriate coefficients must be selected to estimate accurately the amount of dissolved CO2 in

  1. Self-diffusion of magnesium in spinel and in equilibrium melts - Constraints on flash heating of silicates

    NASA Technical Reports Server (NTRS)

    Sheng, Y. J.; Wasserburg, G. J.; Hutcheon, I. D.

    1992-01-01

    An isotopic tracer is used to measure Mg self-diffusion in spinel and coexisting melt at bulk chemical equilibrium. The diffusion coefficients were calculated from the measured isotope profiles using a model that includes the complementary diffusion of Mg-24, Mg-25, and Mg-26 in both phases with the constraint that the Mg content of each phase is constant. The activation energy and preexponential factor for Mg self-diffusion in spinel are, respectively, 384 +/- 7 kJ and 74.6 +/- 1.1 sq cm/s. These data indicate Mg diffusion in spinel is much slower than previous estimates. The activation energy for Mg self-diffusion in coexisting melt is 343 +/- 25 kJ and the preexponential factor is 7791.9 +/- 1.3 sq cm/s. These results are used to evaluate cooling rates of plagioclase-olivine inclusions (POIs) in the Allende meteorite. Given a maximum melting temperature for POIs of about 1500 C, these results show that a 1-micron radius spinel would equilibrate isotopically with a melt within about 60 min.

  2. Glass science tutorial lecture {number_sign}6: The melting of silicate glasses, a review of selected topics

    SciTech Connect

    Swarts, E.L.

    1995-03-01

    This report summarizes a two-day lecture given at Westinghouse Hanford Company in March, 1995 and includes the data used in the presentation. Topics included the special needs of a low-level waste vitrification process, glass melting, mechanisms of the formation of foam, glass refining (bubble removal), and homogenization (reduction of chemical heterogeneity to acceptable levels). 96 refs.

  3. The stability of hibonite, melilite and other aluminous phases in silicate melts: Implications for the origin of hibonite-bearing inclusions from carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Beckett, J. R.; Stolper, E.

    1994-01-01

    Phase fields in which hibonite and silicate melt coexist with spinel CaAl4O7, gehlenitic melilite, anorthite or corundum at 1 bar in the system CaO-MgO-Al2O3-SiO2-TiO2 were determined. The hibonites contain up to 1.7 wt% SiO2. For TiO2, the experimentally determined partition coefficients between hibonite and coexisting melt D(sub i)(sup Hib/L), vary from 0.8 to 2.1 and generally decrease with increasing TiO2 in the liquid. Based on Ti partitioning between hibonite and melt, bulk inclusion compositions and hibonite-saturated liquidus phase diagrams, the hibonite in hibonite-poor fluffy Type A inclusions from Allende and at least some hibonite from hibonite-rich inclusions is relict, although much of the hibonite from hibonite-glass spherules probably crystallized metasably from a melt. Bulk compositions for all of these CAIs are consistent with an origin as melite + hibonite + spinel + perovskite phase assembalges that were partially altered and in some cases partially or completely melted. The duration of the melting event was sufficient to remove any Na introduced by the alteration process but frequently insufficient to dissolve all of the original hibonite. Simple thermochemical models developed for meteoritic melilite and hibonite solid solutions were used to obtain equilibration temperatures of hibonite-bearing phase assemblages with vapor. Referenced to 10(exp -3) atm, hibonite + corundum + vapor equilibrated at approximately 1260 C and hibonite + spinel +/- melilite + vapor at 1215 +/- 10 C. If these temperatures reflect condensation in a cooling gas of solar composition, then hibonite +/- corundum condensed first, followed by spinel and then melilite. The position of perovskite within this sequence is uncertain, but it probably began to condense before spinel. This sequence of phase appearances and relative temperatures is generally consistent with observed textures but differs from expectations based on classical condensation calculations in that

  4. The stability of hibonite, melilite and other aluminous phases in silicate melts: Implications for the origin of hibonite-bearing inclusions from carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Beckett, J. R.; Stolper, E.

    1994-01-01

    Phase fields in which hibonite and silicate melt coexist with spinel CaAl4O7, gehlenitic melilite, anorthite or corundum at 1 bar in the system CaO-MgO-Al2O3-SiO2-TiO2 were determined. The hibonites contain up to 1.7 wt% SiO2. For TiO2, the experimentally determined partition coefficients between hibonite and coexisting melt DiHib/L, vary from 0.8 to 2.1 and generally decrease with increasing TiO2 in the liquid. Based on Ti partitioning between hibonite and melt, bulk inclusion compositions and hibonite-saturated liquidus phase diagrams, the hibonite in hibonite-poor fluffy Type A inclusions from Allende and at least some hibonite from hibonite-rich inclusions is relict, although much of the hibonite from hibonite-glass spherules probably crystallized metasably from a melt. Bulk compositions for all of these CAIs are consistent with an origin as melite + hibonite + spinel + perovskite phase assemblages that were partially altered and in some cases partially or completely melted. The duration of the melting event was sufficient to remove any Na introduced by the alteration process but frequently insufficient to dissolve all of the original hibonite. Simple thermochemical models developed for meteoritic melilite and hibonite solid solutions were used to obtain equilibration temperatures of hibonite-bearing phase assemblages with vapor. Referenced to 10-3 atm, hibonite + corundum + vapor equilibrated at approximately 1260 C and hibonite + spinel +/- melilite + vapor at 1215 +/- 10 C. If these temperatures reflect condensation in a cooling gas of solar composition, then hibonite +/- corundum condensed first, followed by spinel and then melilite. The position of perovskite within this sequence is uncertain, but it probably began to condense before spinel. This sequence of phase appearances and relative temperatures is generally consistent with observed textures but differs from expectations based on classical condensation calculations in that equilibration temperatures

  5. The influence of the conditions of ion exchange in CuSO4:Na2SO4 melt on the optical properties of surface layers of silicate glass

    NASA Astrophysics Data System (ADS)

    Demichev, I. A.; Sidorov, A. I.; Nikonorov, N. V.

    2015-08-01

    The influence of the temperature and duration of ion exchange in BK7 silicate glass in CuSO4:Na2SO4 melt on the optical properties of the glass surface layers has been investigated. It is shown that ion exchange occurs from the melt according to the Cu2+ ↔ 2Na+ scheme. Cu2+ ions penetrate the sample to a depth of about 1 µm. Reduction of Cu2+ ions near the glass surface gives rise to the Cu+ ↔ Na+ ion exchange in the glass. Measurements of refractive index profiles in the glass sample subjected to ion exchange have revealed the formation of two waveguides in the sample: near the surface and at a depth of more than 3 µm; the second waveguide is formed by Cu+ ions. It is shown that relatively low temperatures and short durations of ion exchange lead to the formation of copper molecular clusters Cu n in glass. An increase of ion exchange temperature and duration leads to decomposition of molecular clusters with formation of Cu2+ ions.

  6. Wüstite stability in the presence of a CO2-fluid and a carbonate-silicate melt: Implications for the graphite/diamond formation and generation of Fe-rich mantle metasomatic agents

    NASA Astrophysics Data System (ADS)

    Bataleva, Yuliya V.; Palyanov, Yuri N.; Sokol, Alexander G.; Borzdov, Yuri M.; Bayukov, Oleg A.

    2016-02-01

    Experimental simulation of the interaction of wüstite with a CO2-rich fluid and a carbonate-silicate melt was performed using a multianvil high-pressure split-sphere apparatus in the FeO-MgO-CaO-SiO2-Al2O3-CO2 system at a pressure of 6.3 GPa and temperatures in the range of 1150 °C-1650 °C and with run time of 20 h. At relatively low temperatures, decarbonation reactions occur in the system to form iron-rich garnet (Alm75Prp17Grs8), magnesiowüstite (Mg# ≤ 0.13), and CO2-rich fluid. Under these conditions, magnesiowüstite was found to be capable of partial reducing CO2 to C0 that leads to the formation of Fe3+-bearing magnesiowüstite, crystallization of magnetite and metastable graphite, and initial growth of diamond seeds. At T ≥ 1450 °C, an iron-rich carbonate-silicate melt (FeO ~ 56 wt.%, SiO2 ~ 12 wt.%) forms in the system. Interaction between (Fe,Mg)O, SiO2, fluid and melt leads to oxidation of magnesiowüstite and crystallization of fayalite-magnetite spinel solid solution (1450 °C) as well as to complete dissolution of magnesiowüstite in the carbonate-silicate melt (1550 °C-1650 °C). In the presence of both carbonate-silicate melt and CO2-rich fluid, dissolution (oxidation) of diamond and metastable graphite was found to occur. The study results demonstrate that under pressures of the lithospheric mantle in the presence of a CO2-rich fluid, wüstite/magnesiowüstite is stable only at relatively low temperatures when it is in the absolute excess relative to CO2-rich fluid. In this case, the redox reactions, which produce metastable graphite and diamond with concomitant partial oxidation of wüstite to magnetite, occur. Wüstite is unstable under high concentrations of a CO2-rich fluid as well as in the presence of a carbonate-silicate melt: it is either completely oxidized or dissolves in the melt or fluid phase, leading to the formation of Fe2 +- and Fe3 +-enriched carbonate-silicate melts, which are potential metasomatic agents in the

  7. On the behavior of redox pairs in anhydrous and hydrous silicate melts: from the oxygen electrode to the mutual interactions of Fe and S

    NASA Astrophysics Data System (ADS)

    Moretti, R.

    2005-12-01

    The need of techniques for determining the oxidation state of magmas from iron and/or sulfur redox ratios has pushed scientists to yield composition-based semi-empirical equations, without much interest for the understanding of how electron transfer takes place, thus disregarding true, or at least most plausible, redox exchanges occurring in melts. Not secondary, it has generated notations (i.e., chemical equilibria) in which standard states, species and components are mixed. Let us then go back to basics, by taking the most geologically important element having multiple oxidation states: iron. In order to model redox exchanges we need i) a formalism for acid-base reactions in silicate melts, ii) a reference electrode, iii) a model for computing proportions and activities of species intervening in acid-base exchanges and redox electrodes, including that of reference. Briefly, the above requirements converge in the adoption of the normal oxygen electrode plus the Toop-Samis polymeric approach, which is based on the ionic Temkin notation (Ottonello et al., 2001). Therefore, in silicate melts redox processes and polymerization are intimately related. Under certain conditions, some unexpected features can be explored, such as the oxidation of iron in closed system with decreasing temperature. Let us now complicate the things by introducing the most geologically important volatile: water. Processing of data on the iron redox ratio in hydrous glasses allows one to model the role of composition, temperature, pressure and oxygen fugacity i) by assessing the acid-base properties of the water component in a notation consistent with the above and ii) by introducing volume terms of interest. The central role of water speciation can be then discussed in terms of its amphoteric behavior, in line with the earlier prediction of Fraser (1977) and the recent NMR findings of Xue and Kanzaki (2004). Finally, let us add another multiple valence state element such as S and investigate

  8. Trace element geochemistry of the 1991 Mt. Pinatubo silicic melts, Philippines: Implications for ore-forming potential of adakitic magmatism

    NASA Astrophysics Data System (ADS)

    Borisova, Anastassia Yu.; Pichavant, Michel; Polvé, Mireille; Wiedenbeck, Michael; Freydier, Remi; Candaudap, Frédéric

    2006-07-01

    The dacite pumice erupted from Mt. Pinatubo on June 15, 1991 (whole-rock, rhyolitic groundmass glasses and homogenized melt inclusions) has been analyzed using inductively coupled plasma-mass spectrometry (ICP-MS), nanosecond and femtosecond laser ablation ICP-MS and secondary ion mass spectrometry (SIMS) to evaluate its ore-forming potential. Data suggest that adakite magmas are metal-rich and concentrate ore metals during magmatic differentiation. Sulfides segregate in limited amounts under the hydrous, oxidizing conditions typical of adakitic magmas resulting in incompatible behavior for Au (6-22 ppb), Cu (26-77 ppm), and Pb, Mo, As, and Sb in melts of dacitic to rhyolitic compositions. Metal transfer from this adakite magma to the coexisting aqueous phase was favored by the peraluminous composition of the rhyolitic melt and high aqueous chloride concentrations. Mass balance calculations suggest that the pre-eruptive aqueous phase could have extracted a minimum of 100 t Au and 5 × 10 5 t Cu from the Mt. Pinatubo magma. Our data suggest that intrusives having adakitic signatures are genetically associated with Au-Cu and Cu-Mo mineralization, auriferous porphyry copper deposits, and epithermal gold veins. High H 2O, Cl, Sr/Y, Pb/Ce, Mo/Ce, As/Ce and Sb/Ce in Mt. Pinatubo melts reflect the contribution of deep fluids derived from subducted sediments and altered MORBs in the dacite genesis. The slab-derived fluids carrying mobile elements are likely responsible for the enrichment of adakite magmas in gold, associated metals and H 2O, and may explain the exceptional ore-forming potential of adakite magmatism.

  9. Micro-XANES Measurements on Experimental Spinels and the Oxidation State of Vanadium in Coexisting Spinel and Silicate Melt

    NASA Technical Reports Server (NTRS)

    Righter, K.; Sutton, S. R.; Newville, M.; Le. L.; Schwandt, C. S.

    2005-01-01

    Spinel can be a significant host phase for V which has multiple oxidation states V(sup 2+), V(sup 3+), V(sup 4+) or V(sup 5+) at oxygen fugacities relevant to natural systems. The magnitude of D(V) spinel/melt is known to be a function of composition, temperature and fO2, but the uncertainty of the oxidation state under the range of natural conditions has made elusive a thorough understanding of D(V) spinel/melt. For example, V(sup 3+) is likely to be stable in spinels, based on exchange with Al in experiments in the CaO-MgO-Al2O3-SiO2 system. On the other hand, it has been argued that V(sup 4+) will be stable across the range of natural oxygen fugacities in nature. In order to build on our previous work in more oxidized systems, we have carried out experiments at relatively reducing conditions from the FMQ buffer to 2 log fO2 units below the IW buffer. These spinel-melt pairs, where V is present in the spinel at natural levels (approx. 300 ppm V), were analyzed using an electron microprobe at NASA-JSC and micro- XANES at the Advanced Photon Source at Argonne National Laboratory. The new results will be used together with previous results to understand the valence of V in spinel-melt systems across 12 orders of magnitude of oxygen fugacity, and with application to natural systems.

  10. Trace element partitioning between majoritic garnet and silicate melt at 10-17 GPa: Implications for deep mantle processes

    NASA Astrophysics Data System (ADS)

    Corgne, Alexandre; Armstrong, Lora S.; Keshav, Shantanu; Fei, Yingwei; McDonough, William F.; Minarik, William G.; Moreno, Karen

    2012-09-01

    Melting experiments were performed on a silica-rich peridotite composition at 10-17 GPa to determine majoritic garnet-melt partition coefficients (D) for major and trace elements. Our results show that D for many elements, including Na, Sc, Y and rare earth elements (REE), varies significantly with increasing pressure or proportion of majorite component. Lu and Sc become incompatible at 17 GPa, with D decreasing from 1.5 at 10 GPa to 0.9 at 17 GPa. As predicted from lattice strain, log D for isovalent cations entering the large site of majoritic garnet exhibits a near-parabolic dependence on ionic radius. Our data are used to refine a previously published predictive model for garnet-melt partitioning of trivalent cations, which suffered from a lack of calibration in the 10-20 GPa range. Our results suggest that Archean Al-depleted komatiites from Barberton (South Africa) may have been generated by partial melting of dry peridotite at depths between 200 and 400 km. We also speculate that transition zone diamonds from Kankan (Guinea), which contain inclusions of majoritic garnet, may have formed from the partial reduction of CO2-rich magmas that subsequently transported them to the surface. This hypothesis would provide an explanation for the REE patterns of majoritic garnet trapped within these diamonds, including Eu anomalies. Finally, we show that segregation of majoritic garnet-bearing cumulates during crystallisation of a deep Martian magma ocean could lead to a variety of Lu/Hf and Sm/Nd ratios depending on pressure, leading to a range of ɛ143Nd and ɛ176Hf isotope signatures for potential mantle sources of Martian rocks.