H 2 O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite-periclase equilibrium

Aranovich, L. Ya.; Newton, Robert C.

doi:10.1007/s004100050216

Cited by 204 publications

(116 citation statements)

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“…This is not in agreement with the experimental study of Aranovich and Newton (1996), who found that while a H 2 O was nearly proportional to X H2O in NaCl-H 2 O solutions at 0.2 GPa, with increasing pressure, a H 2 O −X H 2 O relations tended towards a H 2 O ∝ X H 2 O ð Þ 2 . If this were the relationship for our Fig.…”

Section: Relationships With Water Activity a H2ocontrasting

confidence: 91%

The responses of the four main substitution mechanisms of H in olivine to H2O activity at 1050 °C and 3 GPa

Tollan

Smith

O’Neill

et al. 2017

Prog. in Earth and Planet. Sci.

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The water solubility in olivine C H 2 O ð Þ has been investigated at 1050°C and 3 GPa as a function of water activity a H 2 O ð Þ at subsolidus conditions in the piston-cylinder apparatus, with a H 2 O varied using H 2 O-NaCl fluids. Four sets of experiments were conducted to constrain the effect of a H 2 O on the four main substitution mechanisms. The experiments were designed to grow olivine in situ and thus achieve global equilibrium (G-type), as opposed to hydroxylating olivine with a pre-existing point-defect structure and impurity content (M-type). Olivine grains from the experiments were analysed with polarised and unpolarised FTIR spectroscopy, and where necessary, the spectra have been deconvoluted to quantify the contribution of each substitution mechanism. Olivine buffered with magnesiowüstite produced absorbance bands at high wavenumbers ranging from 3566 to 3612 cm −1 . About 50% of the total absorbance was found parallel to the a-axis, 30% parallel to the b-axis and 20% parallel to the c-axis. The total absorbance and hence water concentration in olivine follows the relationship of C H 2 O ∝a H 2 O 2 , indicating that the investigated defect must involve four H atoms substituting for one Si atom (labelled as [Si]). Forsterite buffered with enstatite produced an absorbance band exclusively aligned parallel the c-axis at 3160 cm −1 . The band position, polarisation and observed C H 2 O ∝a H 2 O are consistent with two H substituting for one Mg (labelled as [Mg]). Ti-doped, enstatite-buffered olivine displays absorption bands, and polarisation typical of Ti-clinohumite point defects where two H on the Si-site are charge-balanced by one Ti on a Mg-site (labelled as [Ti]). This is further supported by C H 2 O ∝a H 2 O and a 1:1 relationship of molar H 2 O and TiO 2 in these experiments. Sc-doped, enstatitebuffered experiments display a main absorption band at 3355 cm −1 with C H 2 O ∝a H 2 O 0:5 and a positive correlation of Sc and H, indicating the coupled substitution of a trivalent cation plus a H for two Mg (labelled as [triv]). Our data demonstrate that extreme care has to be taken when inferences from experiments conducted at a H 2 O ¼ 1 are applied to the mantle, where in most cases, a low a H 2 O persists. In particular, the higher exponent of the [Si] substitution mechanism means that the contribution of this hydrous defect to total water content will decrease more rapidly with decreasing a H 2 O than the contributions of the other substitution mechanisms. The experiments confirm previous results that the [Mg] mechanism holds an almost negligible amount of water under nearly all T-PfO 2 -fH 2 O conditions that may be anticipated in nature. However, the small amounts of H 2 O we find in substituting by this mechanism are similar in the experiments on forsterite doped with either Sc or Ti to those in the undoped forsterite at equivalent a H 2 O (all buffered by enstatite), confirming the assumption that, thermodynamically, C H 2 O substituting by each mechanism does not depend on the w...

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Section: Relationships With Water Activity a H2ocontrasting

confidence: 91%

The responses of the four main substitution mechanisms of H in olivine to H2O activity at 1050 °C and 3 GPa

Tollan

Smith

O’Neill

et al. 2017

Prog. in Earth and Planet. Sci.

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“…In contrast, above ∼5 kbar, quartz solubility declines with increasing NaCl concentration at all X NaCl ("salts out"). Halite saturation (dashed line) after Aranovich and Newton (1996). enhancement at the maximum also differ with salt type (Fig.…”

Section: Solubility Of Mineralsmentioning

confidence: 86%

“…According to experimental data (Aranovich (Aranovich and Newton, 1996); (b) H2O-non-polar gas fluids at 700…”

Section: Activity-composition Relations and Petrologic Consequences Omentioning

confidence: 99%

“…Data are from Manning (2006, 2007). Halite saturation (vertical dashed line) after Aranovich and Newton (1996). and Manning, 2000and Manning, , 2009.…”

Section: Solubility Of Mineralsmentioning

confidence: 99%

“…Solubility enhancement is the mole fraction of Ca relative to that in initially pure H2O, as calculated from Manning (2002, 2005), Tropper and Manning (2007) and Antignano and Manning (2008). Halite saturation (vertical dashed line) after Aranovich and Newton (1996). Manning, 2002, 2010).…”

Section: Salt Mineralsmentioning

confidence: 99%

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Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

Manning

Aranovich

2014

Precambrian Research

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a b s t r a c tA number of observations point to the participation of brines in high-grade metamorphic processes. These include findings of alkali and alkaline-earth halides as daughter crystals in fluid inclusions, appreciable concentrations of Cl measured in amphiboles, biotite, scapolite and apatite, and direct observations on high-temperature halides present in the intergranular space in high-grade rocks. This paper reviews some thermodynamic, petrologic and geochemical effects of these brines. Thermodynamic mixing properties of concentrated water-salt fluids at high pressure (P) and temperature (T) differ greatly from those of water-non-polar gas mixtures: the former are characterized by a large negative deviation from ideal solutions, while the latter exhibit positive deviation from ideality. The contrasting behavior has three major petrologic implications. First, compared to mixtures of water and non-polar gases, brines more strongly increase the melting temperature of quartzofeldspathic rocks and more strongly decrease dehydration temperature of water-bearing minerals. This allows a wide P-T window in which subsolidus deep-crustal metasomatism may take place at relatively low H 2 O activity (a H 2 O ) via migrating fluids. In addition, above 2-3 kbar, brine-saturated solidi for simple granite melting show positive dP/dT at constant H 2 O mole fraction (X H 2 O ), favoring ascent of fluid-saturated liquids. Finally, a large miscibility gap exists in H 2 O-CO 2 -salt ternaries at lower crustal conditions, which may concentrate salts in a separate phase and help explain the common observation of CO 2 -rich inclusions in high-grade minerals. We discuss three geochemical consequences of high-grade brines. We report new experimental data on melting of a model granitoid liquid (69 wt% NaAlSi 3 O 8 , 31 wt% SiO 2 ) at 2 kbar in the presence of aqueous NaCl solutions ranging in concentration from a salt mole fraction (X NaCl ) of 0.1-0.3. The results show that Na preferentially partitions into the silicate liquid, enriching the coexisting fluid in HCl. This hydrolysis effect, known previously for granite melts equilibrated with dilute solutions, therefore also extends to more saline brines. Mineral solubilities depend strongly on salt concentration in the coexisting fluid. Below 5 kbar at 700• C, quartz initially salts in with addition of NaCl to H 2 O, reaches a maximum, and then declines; however, it salts out at all X NaCl at higher P. At granulite-facies P-T conditions, the solubilities of other oxide and silicate minerals (corundum, wollastonite, grossular) salt in and then either reach a plateau or salt out slightly at high X NaCl . In contrast, the solubility of Ca-salt minerals increases exponentially with rising X NaCl . The solubility patterns reflect variations in complexing and H 2 O activity in the brine. Partitioning of REE between rock forming minerals and brines, and between felsic melts and brines, differs strongly from that between minerals, melts and water (±non-polar gas). Brines extract REE f...

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Experimental Determination of Calcite Solubility in H ₂ O‐KCl‐NaCl‐LiCl Solutions at 700°C and 8 kbar

Eguchi

2020

Geophysical Monograph Series

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The solubility of calcite in salt-H 2 O fluids was determined at 700 °C and 8 kbar using hydrothermal pistoncylinder methods. The investigated salts included NaCl, KCl, LiCl, and CsCl. Results show that, at constant pressure and temperature, calcite solubility increases with increasing concentration of any individual salt and all investigated salt mixtures. Data regression indicates a simple dependence of solubility on the square of salt mole fraction. At a given salt concentration, solubility enhancement increases with decreasing salt cation size. Experiments on fluids with mixtures of multiple salts were used to derive simple relations that can be used to predict calcite solubility in a wide range of salt solutions at the studied conditions. The results provide a basis for extending this approach to different pressures, temperatures, and salt compositions.

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H 2 O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite-periclase equilibrium

Cited by 204 publications

References 12 publications

The responses of the four main substitution mechanisms of H in olivine to H2O activity at 1050 °C and 3 GPa

The responses of the four main substitution mechanisms of H in olivine to H2O activity at 1050 °C and 3 GPa

Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

Experimental Determination of Calcite Solubility in H ₂ O‐KCl‐NaCl‐LiCl Solutions at 700°C and 8 kbar

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H 2 O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite-periclase equilibrium

Cited by 204 publications

References 12 publications

The responses of the four main substitution mechanisms of H in olivine to H2O activity at 1050 °C and 3 GPa

The responses of the four main substitution mechanisms of H in olivine to H2O activity at 1050 °C and 3 GPa

Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

Experimental Determination of Calcite Solubility in H 2 O‐KCl‐NaCl‐LiCl Solutions at 700°C and 8 kbar

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Product

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Experimental Determination of Calcite Solubility in H ₂ O‐KCl‐NaCl‐LiCl Solutions at 700°C and 8 kbar