Constraints on the Dynamics of Degassing in Basaltic Systems

HR: 13:40h
AN: V13G-01 [Abstracts]
TI: Constraints on the Dynamics of Degassing in Basaltic Systems
AU: * Burton, M R
EM: burton@ct.ingv.it
AF: INGV Catania, Piazza Roma, 2, Catania, CT 95123 Italy
AU: Mader, H M
EM: h.m.mader@bristol.ac.uk
AF: Bristol University, Department of Earth Sciences Wills Memorial Building Queen's Road, Bristol, BS8 1RJ United Kingdom
AU: Polacci, M
EM: polacci@ct.ingv.it
AF: INGV Catania, Piazza Roma, 2, Catania, CT 95123 Italy
AU: Allard, P
EM: patrick.allard@cea.fr
AF: CNRS-CEA, Groupe des Sciences dela Terre Laboratoire Pierre S‘, CE Saclay, 91191 France
AB: Recent advances in our ability to measure the complete composition of volcanic gas emissions using Fourier transform infrared spectrometry, complemented by measurements of dissolved volatile contents in melt inclusions, have allowed deep insights into the degassing process on basaltic volcanoes. One key observation has been the close-to-bulk equilibrium compositions emitted from basaltic systems during quiescent persistent degassing. This suggests that during quiescent periods gas and magma rise together, in chemical equilibrium with one another, with volatiles exsolving during depressurization without being limited by kinetic processes. However, typical original dissolved volatile amounts in basaltic systems are abundant, usually accounting for 3-4wt% of the undegassed magma. This implies that 1m³ of magma arriving at the surface will typically produce ~800m³ of gas. The physical implication of the very high ratio of gas volume to magma volume is that the shallow conduit is filled with a very low density foam, which extends to several kilometres depth. This observation is at odds with products from mild explosive activity, lava effusion and seismic data. In this paper we propose a possible mechanism which produces both equilibrium degassing and lower gas/magma ratios within the conduit. We examine the implications of this mechanism for interpretations of gas composition data and geophysical observations of persistent basaltic systems.
DE: 8400 VOLCANOLOGY
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005