Low-frequency shear and structural relaxation in rhyolite melt

✍ Scribed by Sharon L. Webb

• Publisher: Springer-Verlag
• Year: 1992
• Tongue: English
• Weight: 570 KB
• Volume: 19
• Category: Article
• ISSN: 0342-1791
• DOI: 10.1007/bf00202314

✦ Synopsis

The frequency-dependence of the shear viscosity and modulus of rhyolite melt has been determined over a 10-14 loglo Pa s viscosity range and a 0.03-63 rad s-1 angular frequency range. The frequency-dependent viscosity determined at high frequencies is 5 orders of magnitude lower than the Newtonian viscosity. At lower frequencies, a frequency-independent viscosity identical with the Newtonian viscosity is observed. The measured shear modulus increases from zero to 30.5___2.5 GPa with increasing frequency. The viscoelastic regime consists of a maximum in viscous loss centered on the Maxwell relaxation time. The width and height of the loss modulus as a function of frequency is inconsistent with a single relaxation-time. The frequency-dependent shear modulus is best described by a distribution of relaxationtimes with a sharp cutoff at times slightly longer than the Maxwell relaxation time, and a long tail at shorter times extending up to 5 orders of magnitude less than the Maxwell relaxation time. This distribution of relaxation-times is in contrast with the single-relaxation-time behavior observed in low viscosity silicate melts.