THE ASCENT OF FELSIC MAGMAS IN DYKES

The results of a thermal and fluid-dynamical analysis are presented th at allow geologists to estimate the critical dyke or fracture width (w (c)) necessary for the transport of felsic magma through the crust wit hout control by solidification. The principal geological variables req uired to estimate w(c) are the magmatic viscosity (mu), the density an d temperature contrasts (DELTArho and DELTAT) between magma and countr y rock, and the height of ascent H. The results show that for typical values of mu and DELTArho, and for transport distances of 20 to 30 km, the critical dyke width is constrained to lie between about 2 and 20 m.