The results of a thermal and fluid-dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width (w (sub c) ) necessary for the transport of felsic magma through the crust without control by solidification. The principal geological variables required to estimate w (sub c) are the magmatic viscosity (mu ), the density and temperature contrasts (Delta rho and Delta T) between magma and country rock, and the height of ascent H. The results show that for typical values of mu and Delta rho , and for transport distances of 20 to 30 km, the critical dyke width is constrained to lie between about 2 and 20 m.
Petford, N., Lister, J. R., Kerr, R. C., & Brown, M. (editor). (1994). The ascent of felsic magmas in dykes Crustal anatexis and ascent of felsic magmas. 29th International Geological Congress, 32(1–2), 161–168.