T.M. Seward

Victoria University of Wellington, Wellington, Wellington, New Zealand

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Publications (87)215.75 Total impact

  • Fullerenes Nanotubes and Carbon Nanostructures 08/2015; DOI:10.1080/1536383X.2015.1072515 · 0.84 Impact Factor
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    ABSTRACT: Abstract
    Geochimica et Cosmochimica Acta 04/2015; DOI:10.1016/j.gca.2015.04.009 · 4.33 Impact Factor
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    T.M. Seward · AE Williams-Jones · A.A. Migdisov
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    ABSTRACT: The chapter presents an overview of the chemistry of transport and deposition of metals by aqueous fluids under hydrothermal conditions that are responsible for the formation of ore deposits throughout the Earth's crust. Metal complex equilibria at elevated temperatures and pressures are considered in relation to modern knowledge of water solvent structure and properties as well as electrolyte solution behavior under extreme conditions. The recent advances in our knowledge of the stoichiometry and stability of metal complexes from experimental and ab initio studies are discussed within the context of hydrothermal fluids having liquid-like densities and those having gas-like densities.
    Treatise on Geochemistry, Edited by Heinrich Holland and Karl Turekian, 11/2013: chapter Volume 13: Geochemistry of Mineral Deposits: pages 29-57; Elsevier Ltd.., ISBN: 9780080959757
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    ABSTRACT: Characterising the speciation and solubility of platinum group elements (PGE) in hydrothermal fluids is useful in understanding the formation of PGE deposits, and for supporting the development of new exploration tools for high value magmatic nickel sulfide deposits, whose small footprints may be extended by hydrothermal remobilisation of PGE. A number of experimental studies have investigated Pd speciation and solubility in hydrothermal chloride solutions, with reasonable agreement over the nature and stability of Pd(II) chlorocomplexes (Barnes and Liu, 2012). In contrast, there are significant discrepancies among the available thermodynamic properties for the predominant Pd bisulfide species. This uncertainty severely hinders numerical modelling of PGE mobility in hydrothermal fluids. Ab-initio molecular dynamics (MD) simulations were performed to investigate the stability of possible Pd-Cl and Pd-HS complexes in hydrothermal fluids. The simulations revealed the preference of four-fold square planar structures of both chloride and bisulfide complexes at high P,T (30C, 500 bar). We are building a geochemical model for Pd transport via thermodynamic integration (Mei et al., 2013). The species geometry and thermodynamic properties derived from the MD simulations will be compared with the existing thermodynamic properties (Boily and Seward, 2005) and with new EXAFS measurement of Pd chloride complexes in hydrothermal brines up to 340 ˚C.
    Goldschmidt, Florence, Italy; 08/2013
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    ABSTRACT: Champagne Pool, a sulfidic hot spring in New Zealand, exhibits distinct diurnal variations in antimony (Sb) and arsenic (As) concentrations, with daytime high and night-time low concentrations. To identify the underlying mobilization mechanisms, five sites along the drainage channel of Champagne Pool were sampled every 2 h during a 24 h period. Temporal variations in elemental concentrations and Sb, As, and sulfur (S) speciation were monitored in the discharging fluid. Total trace element concentrations in filtered and unfiltered samples were analyzed using ICP-MS, and Sb, As and S species were determined by IC-ICP-MS. Sulfur speciation in the drainage channel was dominated by thiosulfate and sulfide at night, while sulfate dominated during the day. The distinct diurnal changes suggest that the transformations are caused by phototrophic sulfur-oxidizing bacteria. These bacteria metabolize thiosulfate and sulfide in daylight to form sulfate and, as suggested by modeling with PhreeqC, elemental sulfur. Sulfide consumption during the day results in undersaturation of antimony sulfides, which triggers the additional release of dissolved Sb. For As, diurnal cycles were much more pronounced in speciation than in total concentrations, with di- and trithioarsenate forming at night due to excess sulfide, and monothioarsenate forming from arsenite and elemental sulfur during the day. Sulfur speciation was thus found to control Sb and As in terms of both solubility and speciation.
    Journal of Volcanology and Geothermal Research 07/2013; 262:164-177. DOI:10.1016/j.jvolgeores.2013.07.007 · 2.54 Impact Factor
  • Kono H. Lemke · Terry M. Seward
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    ABSTRACT: The M06-2X and B2PLYP-D functionals have been applied to predict structures and energies for (CO2)n clusters up to n = 16. A comparison between M06-2X, B2PLYP-D and benchmark CCSD(T) results indicates that M06-2X is capable of providing accurate binding energies. Stepwise M06-2X (CO2)n clustering free energies exhibit a sharp discontinuity at the magic cluster size n = 13 and systematically shift to more exergonic values with decreasing temperature, in particular for larger clusters. These results indicate that the M06-2X method provides an accurate and cost effective description of non-covalent interactions in (CO2)n clusters and therefore may provide important information on CO2 nucleation phenomena.
    Chemical Physics Letters 06/2013; 573:19–23. DOI:10.1016/j.cplett.2013.04.044 · 1.90 Impact Factor
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    Liane G. Benning · Terry M. Seward
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    ABSTRACT: The solubility of gold has been measured in aqueous sulphide solutions at temperatures between 150°C and 500°C and pressures of 500–1500 bar over a wide range of pH and total dissolved sulphur concentrations. The solubilities ranged from 0.002–1 mg/kg (1 × 10−8 to 5 × 10−6 m) in experiments with low total sulphur and acid pH, and from 2–108 mg/kg (1 × 10−5 to 5 × 10−4 m) in solutions wit)1 high total reduced sulphur concentrations and near neutral pH. The solubilities generally increased with increasing temperature, pH, and total dissolved sulphur. At near neutral pH, an inverse correlation between solubility and pressure was observed, whereas in acid pH solutions, above 150°C, increasing pressure also increased the solubility.In near neutral pH solutions a solubility maximum was observed. This maximum is due to the species Au(HS)2−. However, with increasing temperature, in accordance with the shift of pK1 of H2S towards more alkaline pH, the maximum solubility also shifts to higher pH-values and consequently, at high temperatures the species stable at lower pH will dominate. It has been unambiguously proven that over a wide range of temperatures and pressures in reduced sulphur-containing hydrothermal solutions of low pH, the stoichiometry of the dominant Au (I)-hydrosulphide complex, is AuHS0. High temperature and high pressure: equilibrium constants for the formation of the Au(I)-hydrosulphide complexes, AuHS0, and Au(HS)2−, pertaining to the equilibria Au(s) + H2S = AuHS0 + H2(g) (1) and Au(s) + H2S + HS− = Au(HS)2− + H2(g), (2) have been calculated. The nonlinear least squares fitted equilibrium constant for reaction (1) varies from log K(1) = −6.81 at 150°C/500 bar to a maximum of −5.90 at 200°C/1500 bar and decreases again at higher temperatures (-7.83 at 400°C/500 bars). For reaction (2), a similar variation occurs: log K(2) = −1.45 at 150°C/500 bar to −1.03 at 250°C/500 bar and −1.75 at 400°C/1500 bar. The thermodynamic functions for the Au(I)-hydrosulphide formation reactions and the cumulative and stepwise formation constants were derived after transforming the above reactions into isocoulombic form.The equilibrium constants were derived after transforming the above reactions into isocoulombic form. role in the transport and deposition of gold in ore depositing environments which are characterised by low pH fluids.
    Geochimica et Cosmochimica Acta 01/2013; 60(11):1849-1871. DOI:10.1016/0016-7037(96)00061-0 · 4.33 Impact Factor
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    ABSTRACT: Adsorbent-trapped volcanic gases, sublimates and condensates from active vents of the La Fossa crater on the island of Vulcano (Aeolian Islands, Italy) as well as ambient and industrial air were quantitatively analyzed by Short-Path Thermal Desorption–Solid Phase Microextraction–Cryotrapping–Gas Chromatography/Mass Spectrometry (SPTD–SPME–CF–GC–MS). Among the over 200 detected and quantified compounds are alkanes, alkenes, arenes, phenols, aldehydes, carboxylic acids, esters, ketones, nitriles, PAHs and their halogenated, methylated and sulfonated derivatives, as well as various heterocyclic compounds including thiophenes and furans. Most compounds are found at concentrations well above laboratory, ambient air, adsorbent and field blank levels. For some analytes (e.g., CFC-11, CH2Cl2, CH3Br), concentrations are up to several orders of magnitude greater than even mid-latitudinal industrial urban air maxima. Air or laboratory contamination is negligible or absent on the basis of noble gas measurements and their isotopic ratios.The organic compounds are interpreted as the product of abiogenic gas-phase radical reactions. On the basis of isomer abundances, n-alkane distributions and substitution patterns the compounds are thought to have formed by high-temperature (e.g., 900 °C) alkyl free radical reactions and halide electrophilic substitution on arenes, alkanes and alkenes. The apparent abiogenic organic chemistry of volcanic gases may give insights into metal transport processes during the formation and alteration of hydrothermal ore deposits, into the natural volcanic source strength of ozone-depleting atmospheric trace gases (i.e., halocarbons), into possibly sensitive trace gas redox pairs as potential early indicators of subsurface changes on volcanoes in the state of imminent unrest, and into the possible hydrothermal origin of early life on Earth, as indicated by the presence of simple amino acids, nitriles, and alkanoic acids.
    Geochimica et Cosmochimica Acta 01/2013; 101:191–221. DOI:10.1016/j.gca.2012.10.004 · 4.33 Impact Factor
  • R. E. Krupp · T. M. Seward
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    ABSTRACT: Mass balance calculations based on metal contents in hot spring mud deposits yield minimum metal contents in hot spring mud deposits yield minimum metal concentrations for the Rotokawa deep geothermal fluid which are compared with calculated (thermodynamic) mineral solubilities and direct analytical metal concentrations. The deep fluid is saturated with respect to native gold and argentite, but unsaturated with respect to cinnabar, native mercury, and stibnite. Adiabatic boiling leads to rapid partial precipitation of argentite from silver chloride complexes while silver and gold bisulfide complexes persist and become unstable only at shallower levels. Stibnite and cinnabar precipitation can only be expected at low temperatures and shallow levels. Mercury partitions into the vapor phase during boiling and a major fraction escapes to the atmosphere.
    Mineralium Deposita 01/2013; 25(1):73-81. DOI:10.1007/BF03326387 · 2.56 Impact Factor
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    ABSTRACT: Trace concentrations of Ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the ‘TitaniQ’ geothermobarometer of Thomas et al. (Contrib Miner Petrol 160:743–759, 2010). It utilises the partitioning of Ti into quartz as an indicator of the pressures and/or temperatures of crystal growth. For a given value of TiO2 activity in the system, if temperatures are inferred to ±20 °C, pressure is constrained to ±1 kbar and vice versa. There are significant contrasts, however, between the conclusions from TitaniQ and those for natural quartz (as well as other mineral phases) in volcanic rocks. Application of the TitaniQ model to quartz from the 27 ka Oruanui and 760 ka Bishop high-silica rhyolites, where the values of T, P and TiO2 activity are constrained by other means (Fe–Ti oxide equilibria, melt inclusion entrapment pressures in gas-saturated melts, melt and amphibole compositions), yields inconsistent results. If realistic values are given to any two of these three parameters, then the value of the third is wholly unrealistic. The model yields growth temperatures at or below the granite solidus, pressures in the lower crust or upper mantle, or TiO2 activities inconsistent with the mineralogical and chemical compositions of the magmas. CL imagery and measurements of Ti (and other elements) in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals, but direct linkages to P, T conditions during crystal growth cannot be achieved.
    Contributions to Mineralogy and Petrology 08/2012; 164(2). DOI:10.1007/s00410-012-0757-1 · 3.48 Impact Factor
  • Valentina P. Zakaznova-Herzog · Terry M. Seward
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    ABSTRACT: The ionization constants of thioarsenous acid have been determined at 22 degrees C by measuring the ultraviolet and visible spectra of thioarsenite species in dilute, aqueous sulfide solutions having S/As = 4.18, As = 1.1 x 10(-4) mol/dm(3) and pH approximate to 6-10.4. No oxidized species such as arsenate, thioarsenate or polysulfides were detected in the experimental solutions. The equilibrium constants for the thioarsenous acid ionization reactions were obtained from a principal component analysis treatment of the spectra and are as follows: H3AsS3 = H+ + H2AsS3- for which pK(a1) = 3.77 (+/- 0.15) H2-AsS32- = H+ + H2AsS3- for which pK(a2) = 6.53 (+/- 0.08) HAsS32- = H+ + AsS33- for which pK(a3) = 9.29 (+/- 0.08) The pK(a)'s for the oxythioarsenous ionization reactions have also been estimated by analogy with those for the end member arsenous and thioarsenous acids. The data emphasize the important role of the simple arsenic(III) thioanions in defining the transport and redox chemistry of arsenic in sulfide-containing natural waters. (C) 2011 Elsevier Ltd. All rights reserved.
    Geochimica et Cosmochimica Acta 04/2012; 83:48-60. DOI:10.1016/j.gca.2011.12.022 · 4.33 Impact Factor
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    N. J. Olsen · B. W. Mountain · T. M. Seward
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    ABSTRACT: Antimony (Sb) is a fluid-mobile element that occurs ubiquitously in geothermal fluids and may occur in surface precipitates of geothermal systems at high concentrations. Antimony sulfide scaling in geothermal power stations is rare but in some places problematic. For example, at the Rotokawa and Ngawha geothermal power stations in New Zealand, cleaning of stibnite scaling in heat exchange units must be done semi-annually and requires temporary closure of the power station. Designing a mitigation strategy for stibnite scaling requires accurate modelling of Sb(III) behavior in geothermal fluids. Accurate modelling requires knowledge of Sb(III) speciation under the relevant temperature, pressure and compositional conditions. Antimony has been known to form hydroxide, chloride and sulfide (thio) complexes in aqueous fluids. The stoichiometry and stability of Sb(III) hydroxide and chloride species are well defined with experimental studies. However, experimental constraints are poor for thioantimonite species in reducing, sulfide-containing, high-temperature geothermal fluids, including those responsible for the formation of epithermal ore deposits. We are determining aqueous Sb speciation in such solutions using solubility experiments. We have conducted solubility experiments using stibnite (Sb2S3) at 25°C in aqueous sulfide solutions. The solubility of stibnite under different pH and sulfide concentrations constrains the Sb:S ratios of the dominant Sb species. Our initial results suggest that previous studies may have overestimated stibnite solubility. Future spectroscopic studies will further refine the stoichiometry of the relevant aqueous species, namely the identity and location of elements complexing with Sb. From these studies we will be able to determine the equilibrium constants of Sb species and will therefore be able to better model Sb behavior in natural systems.
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    ABSTRACT: Fieldwork was conducted in the active north crater of Oldoinyo Lengai volcano, Tanzania. Gases, aqueous fumarole condensates, and freshly erupted natrocarbonatite lavas were collected from several hornitoes associated with the same eruptive center and are considered to represent genetically related products of the same shallow magma chamber. Apparent trace-metal mineral-mineral partition coefficients were derived for the major carbonate phases, gregoryite and nyerereite, and several accessory phases within the fresh lava samples. Trace metals display an affinity for the accessory minerals. Textural information suggests that fluorite and coexisting sylvite are also present interstitially as quenched immiscible salt melts, and that any trace metals present may be scavenged from the carbonatite by the immiscible separation of these salt phases. Gas condensate analyses from the fumaroles associated with the eruption reveal further partitioning of trace elements into the vapor phase. Chalcophile elements show particularly high volatility, and this implies either gas release prior to sulfide formation or the decomposition of sulfides prior to eruption. The strong partitioning of metals into the halogenide and vapor phases has broad implications for the mobility of trace elements in the mantle source, the genesis of exotic mineralization associated with other carbonatites, and the ability of fumarole condensates to carry a direct chemical signature from their parent magma.
    06/2011: pages 159-172;
  • K. Lemke · S. Sadjadi · T. Seward
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    ABSTRACT: The structures and energetic properties of ionic alkali metal halide clusters play a significant role in our understanding of aqueous geochemical processes such as salt dissolution, precipitation and neutralization reactions. Mass spectrometric and quantum chemical studies of such systems offer new opportunities to study the size-dependent evolution of cluster structures, the occurrence of magic number species as well as their fundamental properties. The work here presents new results for the stability, abundance and structure of pure [Na(NaClm)]+ , [K(KCl)m]+ and mixed [Na(NaCl)p(KCl)q]+ metal halide clusters with m<23 and p+q<14, respectively, using ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) in combination with the Gn and CBS-x multistep ab initio methods. Ion-cluster experiments were conducted on a modified 7T Bruker FT-ICR/MS equipped with electrospray ionization (ESI) sources and a custom-designed solvent gas inlet interface. In ESI FT-ICR/MS experiments performed with solutions containing NaCl and KCl salts (1mM; 80/20 CH3CN/H2O), singly and doubly charged salt clusters were generated up to a cluster size of [Na(NaCl)22]+, [K(KCl)17]+ and [K2(KCl)21,23]2+, respectively, including “magic number” clusters that correspond to the completed cluster cuboids with the dimensions 3x3x1 (m=4), 3x3x2+3 (m=10) 3x3x3 (m=13) and 3x3x5 (m=22) (see Figure). On the other hand, no pure clusters except [K(KCl)1-3]+ were generated when alkali halides were electrosprayed from 1mM NaCl/KCl solutions. Instead, mixed [Na(NaCl)p(KCl)q]+ clusters are generated up to p+q=14, which are the largest mixed alkali halide clusters yet generated in mass spectrometric experiments, including a suite of ionic species that are generated via CH3CN fragmentation and charge transfer in [Na(CH3CN)n]+ to yield the clusters [Na(NaCN)(CH3CN)n-1]+. We describe our ESI FT-ICR/MS experiments and discuss ion cluster abundances and extent of clustering in terms of variation of the solvent, desolvation temperature, ESI capillary and cone voltage as well as solution concentration. We also report and compare local minima geometries and relative energies for a number of representative [Na(NaCl)m]+ and [K(KCl)m]+ clusters using the composite CBS-QB3 and G4 methods and comment on the onset of the doubly charged cluster series. FT-ICR mass spectra for [Na(NaCl)n]+ clusters generated from 1mM NaCl in 20%H2O 80% acetonitrile in positive ion mode.
  • C. Wilson · T. Seward · B. L. Charlier · L. Bello · A. Allan
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    ABSTRACT: The concentration of Ti in quartz as an indicator of the temperature conditions of quartz crystallization has gained widespread acceptance since the development of the `TitaniQ' geothermometer of Wark and Watson (2006; Contrib Mineral Petrol 152, 743) and its application in a volcanic context to the Bishop Tuff (Wark et al. 2007; Geology 35, 235). Recent extensions of the TitaniQ model have been made by Thomas et al. (2010; Contrib Mineral Petrol on line, doi:10.1007/s00410-010-0505-3) to incorporate the pressure-dependence of Ti solubility in quartz. Such a geothermobarometer is widespread in application and of interest to workers studying a great variety of crustal rocks. However, there is a significant contrast between the experimental results reported by Thomas et al. (2010) versus conclusions derived from other techniques for the quartz crystals (as well as consistent results from other mineral phases) from silicic volcanic rocks themselves. Here, we draw attention to Ti concentration data from quartz crystals in the 27 ka Oruanui and 760 ka Bishop eruption deposits. In these deposits, other lines of evidence yield pressure estimates for quartz crystal growth at the inferred magmatic temperatures that are between five and ten times less than the lower crustal or upper mantle values derived from the Thomas et al. (2010) formulation. In turn, if pressure estimates for quartz crystallization (from volatile concentrations in gas-saturated melt inclusions) in these examples are taken as accurate then the Thomas et al. (2010) formulation yields temperatures that are demonstrably too low, that is, well below the granite solidus. In either case, the values yielded by the new model are irreconcilable with geological and geophysical observations. Although systematic covariations between Ti concentrations in the experimental quartz crystals and the controlled pressures and temperatures at which they grew have been observed, consideration of the complexities of Ti solubility and speciation in the experimental aqueous fluids suggests that such relationships cannot be simply extrapolated to the natural magmatic environment. The implication is that the theoretical and experimental underpinnings for accurately correlating the Ti contents in magmatic quartz to the temperatures and/or pressures of quartz growth are not soundly based.
  • Z. Minubayeva · T.M. Seward
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    ABSTRACT: This UV spectrophotometric study was aimed at providing precise, experimentally derived thermodynamic data for the ionisation of molybdic acid (H2MoO4) from 30 to 300 °C and at equilibrium saturated vapour pressures. The determination of the equilibrium constants and associated thermodynamic parameters were facilitated by spectrophotometric measurements using a specially designed high temperature optical Ti–Pd flow-through cell with silica glass windows.The following van’t Hoff isochore equations describe the temperature dependence of the first and second ionisation constants of molybdic acid up to 300 °C: The resulting ionisation constants of molybdic acid demonstrate that in low sulphur containing hydrothermal fluids in the Earth’s crust, the transport of molybdenum is favoured by the species while the role of the associated H2MoO4 is of negligible importance at elevated temperatures above 200 °C.
    Geochimica et Cosmochimica Acta 08/2010; 74(15):4365-4374. DOI:10.1016/j.gca.2010.04.054 · 4.33 Impact Factor
  • B. R. Tagirov · T. M. Seward
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    ABSTRACT: The solubility of synthetic ZnS(cr) was measured at 25–250°C and P=150bars as a function of pH in aqueous sulfide solutions (~0.015–0.15m of total reduced sulfur). The solubility determinations were performed using a Ti flow-through hydrothermal reactor. The solubility of ZnS(cr) was found to increase slowly with temperature over the whole pH range from 2 to ~10. The values of the Zn–S–HS complex stability constant, β, were determined for Zn(HS)20(aq), Zn(HS)3−, Zn(HS)42−, and ZnS(HS)−. Based on the experimental values the Ryzhenko–Bryzgalin electrostatic model parameters for these stability constants were calculated, and the ZnS(cr) solubility and the speciation of Zn in sulfide-containing hydrothermal solutions were evaluated. The most pronounced solubility increase, about 3 log units at m(Stotal)=0.1 for the temperatures from 25 to 250°C, was found in acidic solutions (pH~3 to 4) in the Zn(HS)20(aq) predominance field. In weakly alkaline solutions, where Zn(HS)3− and Zn(HS)42− are the dominant Zn–S–HS complexes, the ZnS(cr) solubility increases by 1 log unit at the same conditions. It was found that ZnS(HS)− and especially Zn(HS)42− become less important in high temperature solutions. At 25°C and m(Stotal)=0.1, these species dominate Zn speciation at pH>7. At 100°C and m(Stotal)=0.1, the maximum fraction of Zn(HS)42− is only 20% of the total Zn concentration (i.e. at pHt~7.5), whereas at 350°C and 3
    Chemical Geology 01/2010; 269(3):301-311. DOI:10.1016/j.chemgeo.2009.10.005 · 3.52 Impact Factor
  • Kono H. Lemke · S. K. Butt · Terry M. Seward
    Geochmica et Cosmochimica Acta 06/2009;
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    Kono H. Lemke · Terry M. Seward
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    ABSTRACT: We present results from ab initio calculations for the structures, energetics and atmospheric abundances of neutral clusters containing water, carbon dioxide and nitrous oxide up to 45km altitude using the complete basis set CBS-Q and G3 multi-level procedures. Gas phase hydration energies, enthalpies and entropies for the stepwise attachment of water onto clusters according to X(H2O)n + H2O = X(H2O)n+1 (where X = H2O, CO2 and N2O) are reported for up to n=5. In particular, our results demonstrate that values for the incremental hydration enthalpies and entropies of all three gases H2O, CO2 and N2O asymptotically approach values characteristic of bulk liquid water (i.e. -44.0 kJ/mol for the enthalpy and -118.8 J/Kmol for the entropy of condensation) following attachment of around 3-4 water molecules. Interestingly, our calculated number densities for the water dimer at 292Kelvin are in excellent agreement with recent values obtained from IR measurements of atmospheric media (Pfeilsticker et al., 2003, Science). Our quantum chemical calculations indicate that water attachment onto H2O, CO2 and N2O is a thermodynamically favorable process, such that hydrated clusters would form a significant atmospheric repository of these species.
    Journal of Geophysical Research Atmospheres 10/2008; 113(D19). DOI:10.1029/2007JD009148 · 3.43 Impact Factor
  • A.J. Teague · T.M. Seward · D. Harrison
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    ABSTRACT: Oldoinyo Lengai is the world's only active carbonatite volcano and considerable debate still surrounds the genesis of its magmas. Gases were collected from two fumaroles discharging close to the then active vent in October 2003. Measured fumarole temperatures were ≤ 195°C, despite the nearby, vigorous eruptive activity. Gases were sampled and analysed for noble gas isotopes. Freshly erupted natrocarbonatite lavas, a 1917 nephelinite and a sub-recent wollastonite bearing rock were also collected and analysed for noble gas isotopes using vacuum crushing techniques. In all the lava samples the neon, argon, krypton and xenon isotope ratio data are indistinguishable from air implying atmospheric contamination of the hygroscopic rocks. In the fumaroles, measured 3He/4He ratios are between 4 and 7 R/Ra. This range is similar to published values for silicate xenoliths of the East African Rift implying a local lithospheric mantle source for the volatile component of the Lengai magmas. It is still unclear if the natrocarbonatites themselves come from this region, or if fractionation and/or liquid immiscibility generate the carbonate magmas from a silicate melt within the crust itself.
    Journal of Volcanology and Geothermal Research 08/2008; 175(3):386-390. DOI:10.1016/j.jvolgeores.2008.04.001 · 2.54 Impact Factor

Publication Stats

2k Citations
215.75 Total Impact Points


  • 2010–2013
    • Victoria University of Wellington
      • School of Geography, Environment and Earth Sciences
      Wellington, Wellington, New Zealand
  • 2003–2013
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1989–2013
    • McGill University
      • Department of Earth and Planetary Sciences
      Montréal, Quebec, Canada
  • 2006
    • Lomonosov Moscow State University
      Moskva, Moscow, Russia
  • 2005–2006
    • ETH Zurich
      Zürich, Zurich, Switzerland