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Morizet, Y., Vuilleumier, R. & Paris, M. (2015) A NMR and molecular dynamics study of CO2-bearing basaltic melts and glasses. Chem. Geol. 418 89–103.
Added by: Laurent Cournède (2016-03-10 18:36:40) |
| Type de référence: Article DOI: 10.1016/j.chemgeo.2015.03.021 Numéro d'identification (ISBN etc.): 0009-2541 Clé BibTeX: Morizet2015 Voir tous les détails bibliographiques  |
Catégories: IMN Mots-clés: alkali-silicate-glasses, Aluminosilicate network speciation, calcium aluminosilicate glasses, carbon-dioxide, CO2 speciation, First-principles molecular dynamics simulations, High temperature melt versus glass, high-resolution si-29, high-temperature, MAS NMR, non-bridging oxygen, nuclear magnetic-resonance, piston-cylinder experiments, solid-state si-29, space gaussian pseudopotentials Créateurs: Morizet, Paris, Vuilleumier Collection: Chem. Geol. |
Consultations : 1/607
Indice de consultation : 4% Indice de popularité : 1% |
| Résumé |
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The presence of volatile, especially carbon dioxide (CO2), in silicate liquids is considered as a key parameter to magmatic degassing and eruptive processes. Unfortunately, due to experimental difficulties, our current knowledge on the CO2 effect on silicate melt structure is weak and relies on the observation of ex-situ recovered CO2-bearing glasses. In the present work, we confront the results obtained from NMR spectroscopic observations of glass synthesised at pressure between 0.5 and 3.0 GPa and theoretical investigations from first-principles molecular dynamics (FPMD) simulations conducted at 5.0 and 8.0 GPa on high temperature melt for a simplified basaltic composition. The results obtained on the aluminosilicate framework (molar fraction of silicon species and Al average coordination number) suggest that both ex-situ and in-situ results compare adequately. The results are in agreement with our current knowledge on the change in aluminosilicate melt/glass structure with changing intensive conditions. Increasing pressure from 0.5 to 8.0 GPa induces 1) an increase in the average Al coordination number from 4.1 to almost 5.0 and 2) an increase in the degree of polymerisation with NBO/Si changing from 1.30 to 0.80. The presence of CO2 does not seem to induce a dramatic change on both the average Al coordination number and the NBO/Si. FPMD simulations performed with 0 and 20 wt.\% CO2 at 8.0 GPa result in a change from 4.84 to 4.96 for the average Al coordination number and in a change from 0.87 to 0.80 for the NBO/Si value, respectively. On the contrary, there is a lack of consistency in between the CO2 speciation obtained from NMR spectroscopy and from FPMD simulations. Whereas the analysis of glasses does not reveal the presence of CO2mol species, the FPMD simulation results suggests the existence of a small proportion of CO2mol. Further work with in-situ experimental approach is therefore required to explain the observed lack of consistency between the CO2 speciation in glass and in high temperature melt with basaltic composition. (C) 2015 Elsevier B.V. All rights reserved.
Added by: Laurent Cournède |