HR: 14:40h
AN: V53E-05 INVITED    [Abstracts]
TI: Halogens and melt viscosity: an overview.
AU: * Dingwell, D B
EM: dingwell@lmu.de
AF: Earth and Environment, LMU-University of Munich, Theresienstr. 41/III, Munich, 80333, Germany
AU: Hess, K
EM: Hess@min.uni-muenchen.de
AF: Earth and Environment, LMU-University of Munich, Theresienstr. 41/III, Munich, 80333, Germany
AB: The influence of halogens on melt viscosity ranges from well-investigated, for F, through moderately-well investigated, for Cl, to reconnaissance studies for Br and I. F is the strongest fluxing agent in lavas next to water. It has been investigated and utilised in this capacity for centuries. Under hypabyssal conditions (dykes, small intrusions) fluorine, together with water can dominate melt viscosity. Its relatiively low volatility means that under volcanic conditions of degassed magma, the role of fluorine in controlling lava rheology can be dominant over all other volatiles. Cl is far less effective in influencing melt viscosity than fluorine. Nevertheless, the substantial levels of Cl in aklaine magmas suggest that it should be included in future models. The effect of Cl on melt viscosity has long be argued to generate either slight increase or slight decrease in viscosity. Recent studies indicate that this ambivalent behavior of Cl mnay be a systematic function of melt composition. The influence of Br and I on melt viscosity is at the reconnaissance stage. Nevertheless, the results so far indicate that the Br and I additions achieved so far yield melts with viscosities similar to their halogen-free equivalents. The viscosity data set, will be reviewed and discussed in the context of the relative structural roles of the halogens, their inferred influence on the viscous flow mechanisms and the implications for flow and crystallisation kinetics of magmas and lavas. Together with recent data on the relative diffusivities of F, Cl, Br and I, implications for the degassing kinetics of such systems will also be discussed.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting