[]] [ MINERALS 9 Springer-Verlag 1989 Structural Relaxation in Silicate Melts and Non-Newtonian Melt Rheology in Geologic Processes

Abstract. The timescale of structural relaxation in a silicate melt defines the transition from liquid (relaxed) to glassy (unrelaxed) behavior. Structural relaxation in silicate melts can be described by a relaxation time, z, consistent with the observation that the timescales of both volume and shear relaxation are of the same order of magnitude. The onset of significantly unrelaxed behavior occurs 2 loglo un-its of time above z. In the case of shear relaxation, the relaxation time can be quantified using the Maxwell rela-tionship for a viscoelastic material; Zs=r/s/G ~ (where Zs is the shear elaxation time, G ~ is the shear modulus at infinite frequency and t/s is the zero frequency shear viscosity). The value of Go is known for SiO 2 and several other silicate glasses. The shear modulus, Go, and the bulk modulus, K~, are similar in magnitude for every glass, with bot