HR: 0800h
AN: V41B-0601    [Abstracts]
TI: Halogens behaviours in Magma Degassing: Insights into Eruptive Dynamics, Hydrothermal Systems and Atmospheric Impact of Andesitic Volcanism
AU: * villemant, b
EM: villema@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris - CNRS - Equipe Geologie des systemes volcaniques, 4 place Jussieu, 46-00, 3eme etage, Paris, 75005, France
AU: * villemant, b
EM: villema@ipgp.jussieu.fr
AF: Universite P. et M. Curie, 4 place Jussieu, Paris, 75005, France
AU: Balcone, H
EM: balcone@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris - CNRS - Equipe Geologie des systemes volcaniques, 4 place Jussieu, 46-00, 3eme etage, Paris, 75005, France
AU: Mouatt, J
EM: villema@ipgp.jussieu.fr
AU: Michel, A
EM: michel@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris - CNRS - Equipe Geologie des systemes volcaniques, 4 place Jussieu, 46-00, 3eme etage, Paris, 75005, France
AU: Komorowski, J
EM: komorow@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris - CNRS - Equipe Geologie des systemes volcaniques, 4 place Jussieu, 46-00, 3eme etage, Paris, 75005, France
AU: Boudon, G
EM: boudon@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris - CNRS - Equipe Geologie des systemes volcaniques, 4 place Jussieu, 46-00, 3eme etage, Paris, 75005, France
AB: Shallow degassing of H₂O in andesitic magmas determines the eruptive styles of volcanic eruptions and contributes to the hydrothermal systems developed around active volcanoes. Halogens behaviour during magma degassing primarily depends on their incompatible behaviour in the melts and on water solubility. Thus, residual contents of halogens in volcanic juvenile vitric clasts may be used as tracers of H₂O degassing processes during explosive and effusive eruptions. Because of the large range of water-melt partition coefficients of halogens and their relatively low diffusion coefficients, a comparison of F, Cl, Br and I contents in volcanic clasts in function of their vesicularity and micro-cristallinity allows to precisely model the main degassing processes and to establish constraints on pre-eruptive conditions. Halogens acids (HCl, HBr and HI) extracted in the vapour phase have much more complex behaviours because of their high solubility in low temperature thermal waters, their variable condensation temperatures and their very high reactivity when mixed with low temperature and oxidizing atmospheric gases. A comparison of model compositions of high temperature gases with the composition of thermal waters, and gases from fumaroles or plumes of active volcanoes allows to characterise the shallow volcanic system and its evolutionary states. Variable halogen behaviours are discussed for a variety of eruption types (plinian, vulcanian and dome-forming) and active volcanic systems from the Lesser Antilles (Montagne Pelee, Soufrière of Guadeloupe, Soufriere Hills of Montserrat).
DE: 1065 Major and trace element geochemistry
DE: 8409 Atmospheric effects (0370)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting