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  • 1
    Language: English
    In: Geochimica et Cosmochimica Acta, July 1, 2014, Vol.136, p.126(16)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2014.04.009 Byline: Matthew Steele-MacInnis, Christian Schmidt Abstract: The silicate speciation in H.sub.2O-Na.sub.2O-SiO.sub.2 fluids was studied in situ up to 600[degrees]C and 2.0GPa using Raman spectroscopy and a Bassett-type hydrothermal diamond-anvil cell. Fluid compositions ranged from 3 to 40mol% SiO.sub.2, with various Na/Si ratios. The main trends observed in Raman spectra of fluids with increasing SiO.sub.2 concentration include (1) decrease in the intensity of the [approximately equal to]770cm.sup.-1 band (monomer, Q.sup.0, symmetric stretch); (2) increase in the intensity of the [approximately equal to]1050cm.sup.-1 band (bridging oxygen Si-O-Si antisymmetric stretch) and the bands at [approximately equal to]450-600cm.sup.-1 (bridging oxygen Si-O-Si bending modes); and (3) increase in spectral contributions at [approximately equal to]800-1000cm.sup.-1 from stretching vibrations of Q.sup.1, Q.sup.2 and Q.sup.3 species. These trends are interpreted to represent decrease in the proportion of Q.sup.0 monomers, and increase in the proportions of Q.sup.1 and Q.sup.2 ([+ or -]Q.sup.3) species, with increasing silicate concentration in the fluid up to 40mol% SiO.sub.2. Raman spectra in the range of tetrahedral Si-O stretching vibrations (700-1200cm.sup.-1) exhibit little discernable difference with changing Na/Si ratio, when compared at constant molar concentration of SiO.sub.2. Particularly at lower Na/Si ratio, increasing silicate concentration also results in increasing relative intensity of the Raman signal of O-H stretching vibrations at about 3300cm.sup.-1, suggesting increased intermolecular hydrogen bonding between H.sub.2O molecules and/or oxygen atoms belonging to silicate species. These results suggest that silicate in hydrous fluids in the deep Earth remains occurs predominately as partly polymerized, Q.sup.1 and Q.sup.2 species up to high silicate concentrations, providing an opportune medium for mobilizing high field-strength and other elements in the lithosphere. Article History: Received 12 August 2013; Accepted 7 April 2014 Article Note: (miscellaneous) Associate editor: Gleb S. Pokrovski
    Keywords: Raman Spectroscopy ; Silicates ; Hydrogen
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, August 15, 2013, Vol.115, p.205(12)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2013.04.009 Byline: Matthew Steele-MacInnis, Robert J. Bodnar Abstract: Salinities of aqueous fluid inclusions are commonly determined by measuring the temperatures of dissolution of solid phases (daughter minerals) during heating. The vapor bubble is, in most cases, considered to have no mass and to have no effect on the bulk salinity, owing to the low density of the vapor. In the present study we test the assumption that the vapor bubble can be ignored when estimating salinity based on the halite dissolution temperature. The errors in bulk salinity that result from neglecting the vapor bubble are generally less than [approximately equal to]1.5wt.% NaCl, and errors of this magnitude occur only when there is a large difference between the halite dissolution temperature and the vapor disappearance temperature (e.g., halite dissolution at [approximately equal to]450[degrees]C and vapor bubble disappearance at 800[degrees]C) or, stated differently, when the vapor bubble occupies a significant volume fraction of the inclusion at the temperature of halite disappearance. In most cases errors are less than 0.5wt.% NaCl. Salinity estimated based on T.sub.m,H can be adjusted to account for the contribution of H.sub.2O from the vapor phase, using an empirical relationship describing the proportion of liquid in the inclusion at T.sub.m,H as a function of the difference between T.sub.h,LV and T.sub.m,H. Article History: Received 9 May 2012; Accepted 10 April 2013 Article Note: (miscellaneous) Associate editor: Edward M. Ripley
    Keywords: Salinity ; Rock Salt
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Earth and Planetary Science Letters, March 1, 2012, Vol.321-322, p.139(13)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.epsl.2011.12.037 Byline: Matthew Steele-MacInnis, Liang Han, Robert P. Lowell, J. Donald Rimstidt, Robert J. Bodnar Keywords: seafloor hydrothermal systems; quartz solubility; fluid flow modeling; immiscibility; mineral dissolution and precipitation Abstract: A numerical model describing quartz dissolution and precipitation in sub-seafloor hydrothermal systems has been developed that documents the effects of retrograde quartz solubility and fluid phase immiscibility on the transport and deposition of silica in this environment. Rates of dissolution and precipitation increase with increasing permeability and with increasing maximum temperature at the base of the system. At the most optimal conditions considered in this study (425[degrees]C, permeability of 10.sup.-13 m.sup.2), quartz is precipitated at rates up to 10.sup.-6 mol/m.sup.3*s (equivalent to 700cm.sup.3 of quartz per cubic meter of rock per year). Immiscibility at the base of the system creates a zone in which large amounts of quartz precipitate as a result of phase separation. The high rate of quartz precipitation at the one-fluid-phase/two-fluid phase boundary is consistent with the location of highly silicified zones found beneath volcanogenic massive sulfide deposits. Rapid quartz deposition at this boundary may affect the heat transfer efficiency at the base of the upflow zone and may contribute to immobilizing the brine layer so that it does not rise towards the surface. The process of rapid quartz precipitation at the base of the upflow zone, and its effects on the dynamics of these systems, is only observed under conditions of liquid-vapor immiscibility. Article History: Received 3 May 2011; Revised 5 November 2011; Accepted 26 December 2011 Article Note: (miscellaneous) Editor: T.M. Harrison
    Keywords: Precipitation (Meteorology) -- Analysis ; Permeability -- Analysis ; Hydrothermal Systems (Geology) -- Analysis
    ISSN: 0012-821X
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Geochimica et Cosmochimica Acta, Sept 1, 2012, Vol.92, p.14(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2012.05.044 Byline: Pilar Lecumberri-Sanchez, Matthew Steele-MacInnis, Robert J. Bodnar Abstract: Fluid inclusions (FI) that homogenize by halite disappearance are common in some geological environments, and interpretation of microthermometric data from these inclusions has been limited by the lack of a model describing the PVTX relationships over the complete range of PTX conditions found in nature. In this study, a system of equations has been developed that can be used to estimate salinity, pressure and density of FI that homogenize by halite disappearance. The salinity, pressure, density and dP/dT slope of the FI isochore are calculated as functions of liquid-vapor homogenization temperature (Th) and halite dissolution temperature (Tm). The equations are based on a numerical model describing the isochoric pressure-temperature trajectory followed by halite-saturated fluids during heating. The model is valid for Th and Tm from 100 to 600[degrees]C, and for pressures along the liquid-vapor-halite curve to 300MPa. Author Affiliation: Dept. of Geosciences, 4044 Derring Hall, Virginia Tech, Blacksburg, VA 24061, USA Article History: Received 30 November 2011; Accepted 29 May 2012 Article Note: (miscellaneous) Associate editor: Dimitri A. Sverjensky
    Keywords: Salinity -- Models ; Salinity -- Analysis ; Rock Salt -- Models ; Rock Salt -- Analysis
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 June 2014, Vol.135, pp.354-358
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
    Source: ScienceDirect Journals (Elsevier)
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  • 6
    Language: English
    In: Geochimica et cosmochimica acta, 2013, Vol.115, pp.205-216
    Description: Salinities of aqueous fluid inclusions are commonly determined by measuring the temperatures of dissolution of solid phases (daughter minerals) during heating. The vapor bubble is, in most cases, considered to have no mass and to have no effect on the bulk salinity, owing to the low density of the vapor. In the present study we test the assumption that the vapor bubble can be ignored when estimating salinity based on the halite dissolution temperature. The errors in bulk salinity that result from neglecting the vapor bubble are generally less than ∼1.5wt.% NaCl, and errors of this magnitude occur only when there is a large difference between the halite dissolution temperature and the vapor disappearance temperature (e.g., halite dissolution at ∼450°C and vapor bubble disappearance at 800°C) or, stated differently, when the vapor bubble occupies a significant volume fraction of the inclusion at the temperature of halite disappearance. In most cases errors are less than 0.5wt.% NaCl. Salinity estimated based on Tₘ,H can be adjusted to account for the contribution of H₂O from the vapor phase, using an empirical relationship describing the proportion of liquid in the inclusion at Tₘ,H as a function of the difference between Tₕ,LV and Tₘ,H. ; p. 205-216.
    Keywords: Water ; Sodium Chloride ; Vapors ; Salinity ; Heat ; Minerals ; Temperature
    ISSN: 0016-7037
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 7
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 August 2013, Vol.115, pp.205-216
    Description: Salinities of aqueous fluid inclusions are commonly determined by measuring the temperatures of dissolution of solid phases (daughter minerals) during heating. The vapor bubble is, in most cases, considered to have no mass and to have no effect on the bulk salinity, owing to the low density of the vapor. In the present study we test the assumption that the vapor bubble can be ignored when estimating salinity based on the halite dissolution temperature. The errors in bulk salinity that result from neglecting the vapor bubble are generally less than ∼1.5 wt.% NaCl, and errors of this magnitude occur only when there is a large difference between the halite dissolution temperature and the vapor disappearance temperature (e.g., halite dissolution at ∼450 °C and vapor bubble disappearance at 800 °C) or, stated differently, when the vapor bubble occupies a significant volume fraction of the inclusion at the temperature of halite disappearance. In most cases errors are less than 0.5 wt.% NaCl. Salinity estimated based on can be adjusted to account for the contribution of H O from the vapor phase, using an empirical relationship describing the proportion of liquid in the inclusion at as a function of the difference between and .
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 8
    Language: English
    In: Geochimica et Cosmochimica Acta, 01 July 2014, Vol.136, pp.126-141
    Description: The silicate speciation in H O–Na O–SiO fluids was studied in situ up to 600 °C and 2.0 GPa using Raman spectroscopy and a Bassett-type hydrothermal diamond-anvil cell. Fluid compositions ranged from 3 to 40 mol% SiO , with various Na/Si ratios. The main trends observed in Raman spectra of fluids with increasing SiO concentration include (1) decrease in the intensity of the ∼770 cm band (monomer, Q , symmetric stretch); (2) increase in the intensity of the ∼1050 cm band (bridging oxygen Si–O–Si antisymmetric stretch) and the bands at ∼450–600 cm (bridging oxygen Si–O–Si bending modes); and (3) increase in spectral contributions at ∼800–1000 cm from stretching vibrations of Q , Q and Q species. These trends are interpreted to represent decrease in the proportion of Q monomers, and increase in the proportions of Q and Q (±Q ) species, with increasing silicate concentration in the fluid up to 40 mol% SiO . Raman spectra in the range of tetrahedral Si–O stretching vibrations (700–1200 cm ) exhibit little discernable difference with changing Na/Si ratio, when compared at constant molar concentration of SiO . Particularly at lower Na/Si ratio, increasing silicate concentration also results in increasing relative intensity of the Raman signal of O–H stretching vibrations at about 3300 cm , suggesting increased intermolecular hydrogen bonding between H O molecules and/or oxygen atoms belonging to silicate species. These results suggest that silicate in hydrous fluids in the deep Earth remains occurs predominately as partly polymerized, Q and Q species up to high silicate concentrations, providing an opportune medium for mobilizing high field-strength and other elements in the lithosphere.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 9
    Language: English
    In: Geochimica et Cosmochimica Acta, Jan 1, 2015, Vol.148, p.50(12)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2014.09.026 Byline: Matthew Steele-MacInnis, Pilar Lecumberri-Sanchez, Robert J. Bodnar Abstract: Iron chloride is a common and abundant component in hydrothermal fluids in many geologic environments, yet the thermodynamic and PTx properties of FeCl.sub.2-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 H.sub.2O-FeCl.sub.2. For a given temperature or salinity, the critical pressure in the H.sub.2O-FeCl.sub.2 system is lower than that in the H.sub.2O-NaCl system. In contrast, the critical curves of aqueous solutions of other divalent-cation chlorides, such as MgCl.sub.2 and CaCl.sub.2, 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 FeCl.sub.2-rich fluids. Owing to the low pressure along the critical curve compared to other common aqueous chloride systems, immiscibility of FeCl.sub.2-rich fluids appears to be limited to relatively low pressures, or relatively shallow levels in the crust, compared to other saline hydrothermal fluids. Article History: Received 26 May 2014; Accepted 16 September 2014 Article Note: (miscellaneous) Associate editor: Edward M. Ripley
    Keywords: Hydrothermal Fluids -- Analysis
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 10
    Language: English
    In: The Journal of Chemical Physics, 21 April 2012, Vol.136(15)
    Description: Vibrational spectroscopy techniques are commonly used to probe the atomic-scale structure of silica species in aqueous solution and hydrous silica glasses. However, unequivocal assignment of individual spectroscopic features to specific vibrational modes is challenging. In this contribution, we establish a connection between experimentally observed vibrational bands and ab initio molecular dynamics (MD) of silica species in solution and in hydrous silica glass. Using the mode-projection approach, we decompose the vibrations of silica species into subspectra resulting from several fundamental structural subunits: The SiO 4 tetrahedron of symmetry T d , the bridging oxygen (BO) Si-O-Si of symmetry \documentclass[12pt]{minimal}\begin{document}${\rm C}_{2{\textit v}}$\end{document} C 2 v , the geminal oxygen O-Si-O of symmetry \documentclass[12pt]{minimal}\begin{document}${\rm C}_{2{\textit v}}$\end{document} C 2 v , the individual Si-OH stretching, and the specific ethane-like symmetric stretching contribution of the H 6 Si 2 O 7 dimer. This allows us to study relevant vibrations of these subunits in any degree of polymerization, from the Q 0 monomer up to the fully polymerized Q 4 tetrahedra. Demonstrating the potential of this approach for supplementing the interpretation of experimental spectra, we compare the calculated frequencies to those extracted from experimental Raman spectra of hydrous silica glasses and silica species in aqueous solution. We discuss observed features such as the double-peaked contribution of the Q 2 tetrahedral symmetric stretch, the individual Si-OH stretching vibrations, the origin of the experimentally observed band at 970 cm −1 and the ethane-like vibrational contribution of the H 6 Si 2 O 7 dimer at 870 cm −1 .
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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