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Rôle des éléments alcalins et de l'eau sur les propriétés et la structure des aluminosilicates fondus et vitreux : implications volcanologiques

Charles Le Losq 1
1 Geophysical Laboratory
GC - Géochimie et Cosmochimie
Abstract : During this thesis, we studied the role of alkali elements and water on the structure and properties of aluminosilicates melts and glasses. Those compositions are important for the earth sciences field, and also for the glass-making and ceramic industries. Viscosities of alkali aluminosilicate melts have been measured, and their structures at the short- and middlerange orders have been studied in the corresponding glasses using Raman and NMR spectroscopies. Results show that the viscosity of alkali aluminosilicate melts depends strongly on the M alkali element residing in the network and on the M/Al and the Si/Al ratios. The glass structure changes depending on the M cation. The higher its ionic radius, the stronger it distorts the glass network, and the higher the viscosity is. Vitreous potassium tectosilicates are composed of regions enriched in silica, and of regions enriched in both aluminium and potassium. The potassium could be present in percolation channels in those compositions. The potassium and sodium ions, presenting different ionic radii, do not mix randomly in tectosilicates glasses and melts. This induces strong variations of their rheological properties depending on the sodium/potassium ratio. We implemented a Raman spectroscopy - based protocol allowing measuring the speciation and the concentration of water in aluminosilicate glasses and melts, regardless of their chemical composition. This protocol allows observing the bonding between water and the glass/melt network, and confirms that water have an amphoteric behavior in silicate and aluminosilicates glasses and melts. The application of this new method, in conjunction with the implementation of ad hoc viscosity models of magmas and with the use of geochemistry and geological data, allows us to retrieve pieces of information about the mechanisms controlling the eruptive behavior of volcanoes. This approach have allowed us to better characterized the fragmentation processes that occurred during the 3.1 Ma and 79 AD eruptions of Mont Dore (France) and the Vesuvius (Italy) respectively, and also to bring some pieces of information about the convection process of the Erebus (Antarctica) lava lake.
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Submitted on : Thursday, January 2, 2014 - 9:09:29 PM
Last modification on : Thursday, March 5, 2020 - 7:00:50 PM
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  • HAL Id : tel-00923471, version 1

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Charles Le Losq. Rôle des éléments alcalins et de l'eau sur les propriétés et la structure des aluminosilicates fondus et vitreux : implications volcanologiques. Sciences de la Terre. Université Paris-Diderot - Paris VII, 2012. Français. ⟨tel-00923471⟩

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