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Carbon Dioxide in Synthetic and Natural Silicate Glasses

Citation

Fine, Gerald Jonathan (1986) Carbon Dioxide in Synthetic and Natural Silicate Glasses. Dissertation (Ph.D.), California Institute of Technology. https://resolver.caltech.edu/CaltechTHESIS:09032019-144830666

Abstract

Infrared spectroscopy has been used to study the speciation of CO2 in both synthetic silicate glasses quenched from melts held at high temperatures and pressures and in natural basaltic glasses. In glasses near the NaAlO2-SiO2 join, absorption bands resulting from the antisymmetric stretches of both molecular CO2 (2352 cm-1) and CO2-3 (1610 cm-1 and 1375 cm-1) are observed. The latter are attributed to distorted Na-carbonate ionic-complexes. Molar absorptivities for each of the absorption bands have been determined; these molar absorptivities allow the quantitative determination of species concentrations in sodium aluminosilicate glasses with a precision on the order of several percent of the amount present. The accuracy of the method is estimated to be ±15-20% at present.

The ratio of molecular CO2 to CO2-3 in sodium aluminosilicate glasses varies little for each silicate composition over the range of total dissolved CO2 contents (0-1.5%), pressures (15-33 kbar) and temperatures (1400-1560°C) studied. This ratio is, however, a strong function of silicate composition, increasing both with decreasing Na2O content along the NaAlO2-SiO2 join and with decreasing Na2O content in peraluminous compositions off the join.

The molar absorptivities determined for sodium aluminosilicate glasses have also been used to measure the concentrations of CO2 in albitic (NaAlSi3O8) glasses quenched from melts equilibrated with CO2 vapor at high pressures (15-30 kbar) and temperatures (1450-1625°C). The results show that total CO2 solubility increases with increasing pressure at constant temperature. Both molecular CO2 and CO2-3 concentrations increase with pressure. At constant pressure, the solubility of molecular CO2 decreases with temperature while the concentration of CO2-3 increases. The net effect is that total CO2 solubility is not significantly dependent on temperature, decreasing slightly with increasing temperature at constant pressure.

The speciation of CO2 in both synthetic Ca ± Mg-composition glasses and natural basaltic glasses contrasts with the case of CO2-bearing sodium aluminosilicate glasses. CO2 is inferred to be dissolved in these glasses as distorted Ca- or Mg-carbonate ionic-complexes that result in unique infrared absorption bands at 1515 cm-1 and 1435 cm-1. The molar absorptivities for each of these absorption bands were also determined. No detectable molecular CO2 is dissolved in these glasses.

Infrared spectroscopic measurements of species concentrations in glasses provide insights into the molecular level processes accompanying CO2 solution in melts and can be used to test and constrain thermodynamic models of CO2-bearing melts. CO2 speciation in silicate melts can be modelled by equilibria between molecular CO2, CO2-3, and oxygen species in the melts. Consideration of the thermodynamics of such equilibria can account for the observed linear relationship between molecular CO2 and carbonate concentrations in sodium aluminosilicate glasses, the absence of molecular CO2 in Ca ± Mg silicate glasses, the proposed linear relationship between total dissolved CO2 content and the activity of CO2 in melts, and observed variations in CO2 solubility in melts.

Dissolved CO2 contents of natural basaltic glasses can also be determined from the intensities of the carbonate absorption bands at 1515 cm-1 and 1435 cm-1. The uncertainty of the method is estimated to be ±15% of the amount present. The infrared technique is a powerful tool for the measurement of dissolved CO2 contents in natural basaltic glasses since it is nondestructive, can be aimed at regions of glass a few tens of micrometers in size, and discriminates between dissolved carbonate and carbon present as carbonate alteration, contained in fluid inclusions or adsorbed on the glass.

A set of submarine basaltic glasses dredged from a variety of locations contain 0-400 ppm dissolved CO2, measured using the infrared technique. These concentrations are lower than most previous reports for similar basaltic glasses. No general relationship is observed between dissolved CO2 content and depth of magmatic eruption.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Geology
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Stolper, Edward M.
Thesis Committee:
  • Rossman, George Robert (chair)
  • Stolper, Edward M.
  • Wyllie, Peter J.
  • Ahrens, Thomas J.
  • Burnett, Donald S.
  • Epstein, Samuel
Defense Date:15 November 1985
Funders:
Funding AgencyGrant Number
NSFEAR-8212765
NSFEAR-8417434
Record Number:CaltechTHESIS:09032019-144830666
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:09032019-144830666
Related URLs:
URLURL TypeDescription
https://doi.org/10.1007/bf00377759DOIArticle adapted for Chapter 1.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11789
Collection:CaltechTHESIS
Deposited By: Melissa Ray
Deposited On:04 Sep 2019 23:31
Last Modified:02 Dec 2020 01:38

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