Davis, M., Koenders, M.A. and Petford, N., 2005. Earthquake-excited crystal rich magmas. In: American Geophysical Union, Fall Meeting 2005, 5-9 Dec 2005, San Francisco, USA.
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We present the results of a novel set of calculations into the effect of in-situ pressure reduction of a crystal-rich, crustal magma chamber by propagating seismic (P) waves. Three stages in the process are identified. Critically, an instability can arise such that a fluidized, low pressure melt layer develops close to the floor in initially densely packed magma (Φ = 0.6) on near-instantaneous timescales. The role of particle pressure, a newly identified force arising from interactions between adjacent crystals in the magma, is fundamental to the development of the instability, which will not arise in crystal-free liquids. Key variables governing the instability are identified and include the mean particle diameter, the excitation frequency (1-10 Hz), interstitial melt viscosity and melt compressibility. Small penetration depths (high particle pressures) develop most readily in compressible, volatile-bearing magmas at higher frequencies. The quasi-static particle pressure that develops as a result of the spatially-decaying oscillations leads to two effects: 1) a rapid reduction in the interstitial melt pressure (c.0.16 MPa/s) resulting in heterogeneous bubble nucleation, and 2) fluidization of a thin layer at the base of the magma chamber. Both these effects in turn increase the particle pressure. The fluidization effect provides a way of rapidly segregating crystals from interstitial liquid (mechanical differentiation) to produce a potentially unstable melt-rich layer at the chamber floor with a viscosity interval (η) in the range 102 < η <103 Pa s. A non-linear runaway effect is identified, driven by positive feedback between particle pressure, melt viscosity and degassing.
|Item Type:||Conference or Workshop Item (Paper)|
|Additional Information:||Abstract #V24B-02|
|Subjects:||Science > Earth Sciences|
|Group:||University Executive Team|
|Deposited By:||Ms MJ Bowden|
|Deposited On:||02 Jan 2008|
|Last Modified:||07 Mar 2013 14:44|
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