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Martin L.H.J.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Martin L.H.J.,Institute for Geochemistry and Petrology | Winnefeld F.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Tschopp E.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 2 more authors.
Cement and Concrete Research | Year: 2017

The effect of fly ash on the hydration of calcium sulfoaluminate cement was investigated. Increasing fly ash contents accelerated the hydration of calcium sulfoaluminate cement due to the filler effect. Dissolution rims around fly ash particles after 90 days indicated a reaction degree of the fly ash of approximately 20 to 30% as estimated by various independent methods. The contribution of fly ash to the hydration reactions resulted in the formation of C-S-H, in an increase of the strätlingite content and in the destabilization of monosulfate. The mortar with 7.5 mass-% fly ash reached a higher compressive strength than the reference without fly ash when the water to cement ratio was kept constant. Up to 15 mass-% of fly ash could be added without strength loss. © 2017 Elsevier Ltd

Steele-Macinnis M.,University of Arizona | Steele-Macinnis M.,Institute for Geochemistry and Petrology | Reimer J.,Paul Scherrer Institute | Bachmann S.,ETH Zurich
RSC Advances | Year: 2015

Molecular simulations have been conducted to assess the pVT properties and static permittivity of the charge-on-spring polarizable water model COS/D2 at hydrothermal conditions from 300 to 450 °C and bulk densities of 0.001 to 1.0 g cm-3. The results indicate that the model performs well for reproducing volumetric and dielectric properties of real water. The liquid-vapor coexistence curve and critical point of COS/D2 water (ca. 334 °C, 21.7 MPa and 0.32 g cm-3) are also in reasonable agreement with those of real water (ca. 374 °C, 22.1 MPa and 0.322 g cm-3). We include comparisons to other polarizable (as well as non-polarizable) water models where available. The good performance of the COS/D2 model at high temperatures and pressures is noteworthy considering that the model was parameterized exclusively at room temperature and pressure. Moreover, these results imply that COS/D2 is a suitable water model for simulating solutions of non-electrolyte and electrolyte solutes at elevated temperatures and pressures. © The Royal Society of Chemistry 2015.

Steele-MacInnis M.,University of Arizona | Steele-MacInnis M.,Institute for Geochemistry and Petrology | Ridley J.,Colorado State University | Lecumberri-Sanchez P.,University of Arizona | And 3 more authors.
Earth-Science Reviews | Year: 2016

Fluid inclusions are commonly the best available source of information on the compositions of fluids in past geologic environments. Microanalytical data, predominantly from LA-ICPMS, allow assessment of the relative abundances of chemical elements in fluid inclusions. Such data show that geologic fluids commonly contain appreciable concentrations of multiple salts in addition to NaCl, particularly KCl, CaCl2, and FeCl2 as major components. Quantification of absolute salt concentrations generally requires an internal standard concentration, which is typically derived from microthermometric measurements interpreted according to the vapor-saturated liquidus relations of simpler systems such as H2O-NaCl or H2O-NaCl-CaCl2. Here, we review and reassess compositional information obtainable from microthermometric measurements in multicomponent chloride-dominated aqueous systems. To do so, we investigate the systematics of vapor-saturated liquidus phase equilibria in complex multicomponent electrolyte solutions through thermodynamic modeling based on Pitzer's equations. We focus on low- to intermediate-salinity chloride-dominated inclusions, in which ice is the liquidus phase, and on the temperature range from subsolidus conditions to <25 °C. On the basis of measured ice and hydrohalite melting temperatures, fluids with predominantly monovalent (Na ± K) chlorides, or mixtures of monovalent and divalent cation chlorides can be identified and a robust value of mNa as a proportion of total cations be calculated. We show that microthermometric measurements alone do not allow unequivocal determination of the identity of salts that are present in addition to NaCl. In combination with microanalytical determination of cation ratios, however, robust compositional results for multi-salt aqueous fluid inclusions can be obtained using microthermometric measurements interpreted with generic H2O-(Na,K)Cl-σXn+Cln phase stability relations. © 2016 Elsevier B.V.

Mantegazzi D.,Institute for Geochemistry and Petrology | Sanchez-Valle C.,Institute for Geochemistry and Petrology | Driesner T.,Institute for Geochemistry and Petrology
Geochimica et Cosmochimica Acta | Year: 2013

NaCl is the most common solute in aqueous fluids in many geological settings but the thermodynamic properties of binary NaCl-H2O solutions have remained understudied at pressures above 0.5GPa. We report the first high-pressure (>0.5GPa) density data for NaCl-H2O fluids derived from acoustic velocity measurements in 1m and 3m NaCl solutions in diamond anvil cells to 673K and 4.5GPa using Brillouin scattering spectroscopy. An empirical equation of state (EoS) for NaCl-H2O fluids has been generated fitting the new density data together with literature data for water, and used for extrapolation of thermodynamic data to 1073K and 4.8m NaCl at 0.5-4.5GPa, spanning the conditions for fluids expelled by subducted slabs. The EoS yields densities for binary NaCl-H2O solutions with uncertainty lower than 0.3-0.5% below 673K and lower than 2-4% in the extrapolation region. The EoS may allow extrapolations beyond 1073K although the resulting uncertainties are difficult to assess. Densities for NaCl-H2O fluids computed from the EoS at 0.5GPa generally agree within 1% with published data below 673K, although differences of up to 5% are observed at 1073K. The experimentally-based EoS is more reliable in the calculation of pure water fugacities and phase equilibria involving fluid phases than previous formulations, particularly in the high pressure range. The presence of dissolved NaCl substantially decreases the activity of water, indicating large non-ideality in NaCl aqueous fluids at subduction zone conditions. This behavior has important implications for the localization of dehydration reactions in the slab, as the dehydration boundaries of hydrous phases shift toward shallower depths in the presence of dissolved NaCl in the fluid. © 2013 Elsevier Ltd.

Louvel M.,Institute for Geochemistry and Petrology | Sanchez-Valle C.,Institute for Geochemistry and Petrology | Malfait W.J.,Institute for Geochemistry and Petrology | Testemale D.,CNRS Neel Institute | Hazemann J.-L.,CNRS Neel Institute
Geochimica et Cosmochimica Acta | Year: 2013

Field observations and solubility experiments show evidence for the efficient mobilization of nominally insoluble HFSE (i.e., Ti, Zr, Nb and Hf) by high pressure fluids, probably via complexation with polymerized alkali-silica dissolved species and halogens (F and Cl). Here we investigate the complexation of Zr in subduction-related fluids (aqueous fluids and hydrous haplogranite melts) up to 800°C and 2.4GPa using X-ray absorption spectroscopy (XANES and EXAFS) in a hydrothermal diamond anvil cell and provide evidence for the formation of Zr-O-Si/Na polymeric species in alkali-(alumino)silicate fluids at high pressure. Zr4+ speciation in dilute fluids (2.5wt% HCl) is dominated by 8-fold-coordinated [Zr(H2O)8]4+ hydrated complexes at room conditions and no evidence for extensive Zr-Cl complexation in the fluid was found up to 420°C, as confirmed by ab initio XANES calculations of various ZrO8-xClx clusters. The addition of Na and Si dissolved species (from 35 to 60wt% dissolved Na2Si2O5, NS2) into the fluid favors the formation of alkali-zirconosilicate clusters Zr-O-Si/Na similar to those found in vlasovite (Na2ZrSi4O11), with Zr4+ in octahedral coordination with oxygen (Zr-O distance=2.09±0.04å) and ∼6 Si (Na) second neighbors (Zr-Si/Na distance=3.66±0.06å). This coordination environment also dominates Zr speciation in F-free and F-bearing NS2 and haplogranite glasses and high pressure hydrous haplogranite melts (15.5-33wt% dissolved H2O) in the investigated pressure-temperature range. The XAS analyses, assisted by ab initio XANES calculations, are not conclusive concerning the extent of Zr-F complexation in hydrous granitic melts. Alkali-zirconosilicate Zr-O-Si/Na clusters such as those identified in this study may explain the enhanced solubility of zircon ZrSiO4 (and other HFSE-bearing minerals) in alkali-aluminosilicate-bearing aqueous fluids produced by dehydration and melting of the slab and provide a favorable mechanism for the mobilization of HFSE in subduction zones. Fluid-rock interactions and/or P/T variations as fluids migrate through the mantle wedge could affect the stability of these complexes, triggering the precipitation of HFSE-bearing accessory phases that are eventually recycled into the mantle, contributing to the dispersion of HFSE. These processes provide a possible explanation for the characteristic HFSE depletion recorded in arc magmas. © 2012 Elsevier Ltd.

Steele-MacInnis M.,Virginia Polytechnic Institute and State University | Steele-MacInnis M.,Institute for Geochemistry and Petrology | Lecumberri-Sanchez P.,Virginia Polytechnic Institute and State University | Lecumberri-Sanchez P.,Institute for Geochemistry and Petrology | Bodnar R.J.,Virginia Polytechnic Institute and State University
Geochimica et Cosmochimica Acta | Year: 2015

Iron chloride is a common and abundant component in hydrothermal fluids in many geologic environments, yet the thermodynamic and PTx properties of FeCl2-bearing aqueous fluids are poorly known. In this study we have used the synthetic fluid inclusion technique to characterize the PTx conditions along the critical curve of the system H2O-FeCl2. For a given temperature or salinity, the critical pressure in the H2O-FeCl2 system is lower than that in the H2O-NaCl system. In contrast, the critical curves of aqueous solutions of other divalent-cation chlorides, such as MgCl2 and CaCl2, are at higher pressure than that of NaCl solutions of equivalent temperature or salinity. The results of this study provide the first quantitative constraints on the PTx extent of liquid-vapor immiscibility for FeCl2-rich fluids. Owing to the low pressure along the critical curve compared to other common aqueous chloride systems, immiscibility of FeCl2-rich fluids appears to be limited to relatively low pressures, or relatively shallow levels in the crust, compared to other saline hydrothermal fluids. © 2014 Elsevier Ltd.

Moore J.M.,Rhodes University | Kuhn B.K.,Rhodes University | Kuhn B.K.,Institute for Geochemistry and Petrology | Mark D.F.,Scottish Universities Environmental Research Center | Tsikos H.,Rhodes University
European Journal of Mineralogy | Year: 2011

An occurrence of the alkali-rich, Fe-Mn silicate sugilite [KNa 2(Fe3+, Mn3+, Al)2Li 3Si12O30] is reported from the Wolhaarkop manganese-rich chert breccia at the Bruce iron-ore mine, Northern Cape Province, South Africa. The upper portion of the breccia is dominated by braunite, albite, K-feldspar and aegirine, and locally hosts irregular-shaped void-fills (generally <5 cm) consisting of both zoned and unzoned assemblages of alkali-rich Mn-silicates. The zoned void-fills are characterised by marginal needles of a mineral with norrishite-like composition [KMn3+ 2LiSi4O10(O)2] penetrating into a persistent wall zone that comprises tabular serandite [NaMn2Si 3O8(OH)], albite, K-feldspar and lesser granular sugilite. The cores of larger vugs are occupied by masses of interlocking armbrusterite [K5Na6Mn3+Mn2+14(Si 9O22)4(OH)10.4H2O] and/or fibrous sugilite. Unzoned assemblages contain a similar mineralogy, comprising albite, K-feldspar, quartz, sugilite, norrishite, serandite, armbrusterite and minor witherite, strontianite and kentrolite [PbMn2O 2(Si2O7)]. Similarities to sugilite-bearing assemblages at the Wessels mine in the Kalahari Manganese Field suggest that a single regional hydrothermal alteration event in the vicinity of the unconformity between the Olifantshoek and Transvaal Supergroups was the probable genetic cause for both occurrences. 40Ar-39Ar dating of fibrous sugilite, however, yields an age of 620.2 ± 3.3 Ma (2σ) that is distinctly younger than the ages reported for the assemblages from the Kalahari Manganese Field. © 2011 E. Schweizerbart'sche Verlagsbuchhandlung.

Martin J.E.,University of Bristol | Martin J.E.,Ecole Normale Superieure de Lyon | Vance D.,Institute for Geochemistry and Petrology | Balter V.,Ecole Normale Superieure de Lyon
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Geochemical inferences on ancient diet using bone and enamel apatite rely mainly on carbon isotope ratios (δ13C) and to a lesser extent on strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) elemental ratios. Recent developments in nontraditional stable isotopes provide an unprecedented opportunity to use additional paleodietary proxies to disentangle complex diets such as omnivory. Of particular relevance for paleodietary reconstruction are metals present in large quantity in bone and enamel apatite, providing that biologically mediated fractionation processes are constrained. Calcium isotope ratios (δ44Ca) meet these criteria but exhibit complex ecological patterning. Stable magnesium isotope ratios (δ26Mg) also meet these criteria but a comprehensive understanding of its variability awaits new isotopic data. Here, 11 extant mammal species of known ecology from a single locality in equatorial Africa were sampled for tooth enamel and, together with vegetation and feces, analyzed for δ26Mg, δ13C, Sr/Ca, and Ba/Ca ratios. The results demonstrate that δ26Mg incorporated in tooth enamel becomes heavier from strict herbivores to omnivores/ faunivores. Using data from experimentally raised sheep, we suggest that this 26Mg enrichment up the trophic chain is due to a 26Mg enrichment in muscle relative to bone. Notably, it is possible to distinguish omnivores from herbivores, using δ26Mg coupled to Ba/Ca ratios. The potential effects of metabolic and dietary changes on the enamel δ26Mg composition remain to be explored but, in the future, multiproxy approaches would permit a substantial refinement of dietary behaviors or enable accurate trophic reconstruction despite specimen-limited sampling, as is often the case for fossil assemblages.

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