RHEOLOGY AND RUPTURE OF HOMOGENEOUS SILICATE LIQUIDS AT MAGMATIC TEMPERATURES

Homogeneous silicate liquids have a Newtonian rheology under condition s of modest stress, but under relatively high stress or otherwise impo sed high rates of deformation their viscosity may become non-Newtonian before the onset of rupture. This behavior has been discussed semi-em pirically as well as in terms of the Maxwell model liquid. Here it is shown that the configurational entropy theory for the occurrence of th e glass transition can also explain this non-Newtonian rheology of sil icate liquids ranging in composition from silica-rich to silica-poor. The pressure and temperature dependence of the transition from Newtoni an to non-Newtonian flow is discussed qualitatively. Geological applic ations are indicated. Fragmentation of silicate liquids takes place wh en the glass transition is crossed and the liquid has become solid lik e. Experimental evidence indicates that the rupture strength is only s lightly larger than the stress needed to cause the onset of non-Newton ian rheology.