Experiments on upward migration of a liquid-rich layer in a granular medium: Implications for a crystalline magma chamber

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2012-03, Vol.13 (3), p.np-n/a
• Main Authors: Shibano, Yasuko, Namiki, Atsuko, Sumita, Ikuro
• Format: Article
• Language: English
• Subjects: Boundary layers; Chambers; Convection; Crystal structure; Crystals; Diapirs; dilation; Geology; granular media; Liquids; Magma; magma chamber; melt transport; Migration; Mineralogy; Petrology; Physical properties; reactivation; Rocks; Settling; Stokes law (fluid mechanics); Transport
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2011GC003994

We perform a series of experiments to investigate the situation in which a melt‐rich layer formed by a magma intrusion ascends through a crystalline magma chamber. The initial condition is such that a heavier granular layer overlies a liquid layer. The particles consisting the upper granular layer are in a jammed state, and only the particles near the interface can move to form a dilated boundary layer. The dilated layer detaches from the upper granular layer, and forms downwelling plumes which drive a cellular convection within the liquid‐rich layer. The convection erodes the upper granular layer, and the liquid‐rich layer migrates upwards with time. This upward migration of the liquid‐rich layer differs from the previously known mechanisms of liquid transport; permeable flow in which the liquid migrates at the Darcy velocity, the Stokes settling in which the individual particle settles, and diapirs formed by the Rayleigh‐Taylor instability. We find that the velocity of the upward migration of the liquid‐rich layer can be scaled by the volumetric flux of the liquid ascending through the narrow channel between the particles. The upward migration of the liquid‐rich layer is faster than the Darcy velocity. In a mushy magma chamber whose crystals are in a jammed state, neither the Stokes settling nor the Rayleigh‐Taylor instability can occur. We propose that the upward migration of the melt‐rich layer observed in our experiments can become an efficient mechanism of melt transport in a crystalline magma chamber. Key Points We discover a new mechanism to transport melt in a crystalline mush The melt‐rich layer migrates upwards by eroding the upper granular layer The upward migration can be faster than the permeable flow and diapiric ascent