Our work on magma chamber processes is a collaborative effort with Calvin Miller and his students. It is aimed at clarifying how certain fluid transport phenomena, including fluid-grain interactions and fluid stirring and mixing, might contribute to the complex architecture observed in well exposed plutons in southern Nevada. Our current work combines theory with scaled laboratory experiments in support of the field mapping and analytical work of Miller's group.
Low-viscosity glycerin (red) moving as a gravity flow into less dense high-viscosity silicon fluid (clear); viscous planing of the flow front "traps" a boundary sublayer beneath the glycerin.
Magma Emplacement
We are currently conducting dynamically scaled laboratory experiments to mimic certain features of emplacement of mafic magma layers into a felsic host. These experiments are part of the thesis work of Heather Bleick. The viscosity contrasts and characteristic lengthscales in our experiments place them in the "nose-splitting" regime of Snyder and Tait (J. Fluid. Mech., 369, 1-21). A scaling analysis indicates that sublayer fluid is not so much "squeezed" out by the overlying denser fluid as it is "dragged" out by the motion of this overlying fluid.
Bleick, H. A., Miller, C. F. and Furbish, D. J. Intrusion of a mafic magma layer into a felsic magma host: Development and behavior of a felsic sublayer. (in preparation)
Miller, C. F., Furbish, D. J., Miller, J. S. and Faulds, J. E. 2005. Daly Lecture: Transport, deposition, storage, and remobilization of felsic magmas and their products in the upper crust. Eos. Trans. AGU, 86(18).
Miller, C. F., Furbish, D. J., Bleick, H. A., Koteas, G. C., Walker, B. A. and Miller, J. S. 2004. Magma chambers as depositional systems. Abstracts with Program, Geological Society of America, Denver.
Rayleigh-Taylor instability manifest as waveforms in the glycerin-silicon fluid interface (above); the waveforms grow into pipe-like features (below) that transport sublayer fluid upward through the glycerin, eventually "draining" the sublayer.
Rayleigh-Taylor Instabilities and Pipe Growth
The emplacement of a relatively dense fluid ("mafic magma") over a less dense fluid ("felsic material") is a mechanically unstable condition. Our experiments reveal the onset of Rayleigh-Taylor instabilities, which may represent the initial growth of scaled analogues of felsic pipes that intrude upward through mafic layers. The fastest-growing wavelengths predicted by linear stability theory match the wavelengths of fluid-interface waveforms in our experiments, and approximately coincide with the spacing of felsic pipes observed in the field.
