HR: 08:30h
AN: V11A-03    [Abstracts]
TI: A new Model for Crystallization and Differentiation in Magma Chambers
AU: * MICHAUT, C
EM: michaut@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, place Jussieu BP 89, PARIS, 75252 France
AU: JAUPART, C
EM: cj@ccr.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, place Jussieu BP 89, PARIS, 75252 France
AB: How magma reservoirs cool and crystallize is intimately related to how they form and grow. We present a new model of magma accumulation and crystallization due to successive magma injections which accounts for the kinetics of crystal nucleation and growth. In this model, magma reservoirs develop out of sill or dyke complexes. For a thin dyke or sill, cooling proceeds faster than crystal nucleation and growth, implying glass formation. Successive injections thus lead to the accumulation of uncrystallized magma. Temperatures in the sill or dyke complex increase gradually with each injection until they become large enough to allow crystal nucleation and growth. In such a system, crystals are generated as temperatures rise. Our calculations show that crystallization is sudden and massive, affecting most of the stored magma, due to a positive feedback between latent heat release and crystallization (i.e. opposite to what occurs in a cooling sequence). The crystal population includes early crystals of primitive composition generated at each injection and late crystals spanning a large compositional range due to the massive crystallization event. At Earth's surface, the eruption record would thus be characterized by a series of primitive lavas, corresponding to the discrete injection events, followed by a large volume of evolved lava, corresponding to the residual melt generated by the massive crystallization event. Following the massive crystallization event, subsequent magma injections lead to an episodic crystallization evolution, with a different compositional trend.
DE: 8400 VOLCANOLOGY
DE: 8411 Thermodynamics (0766, 1011, 3611)
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005