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Webb & Dingwell 1990
Webb, S.L. and Dingwell, D.B. (1990). Non-newtonain rheology of igneous melts at high stresses and strain rates: experimental results for rhyolite, andesite, basalt, and nephelinite. Journal of Geophysical Research 95: doi: 10.1029/90JB00247. issn: 0148-0227.

The stress-strain rate relationships of four silicate melt compositions (high-silica rhyolite, andesite, tholeiitic basalt, and nephelinite) have been studied using the fiber elogation method. Measurements were conducted in a stress range of 10--400 MPa and a strain rate range of 10-6 to 10-3 s-1. The stress-strain rate relationships for all the melts exhibit Newtonian behavior at low strain rates, but non-Newtonian (nonlinear stress-strain rate) behavior at higher strain rates, with strain rate increasing faster than the applied stress. The decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt. The decrease in viscosity observed at the high strain rates of the present study ranges from 0.25 to 2.54 log10f Pa s. The shear relaxation times &tgr; of these melts have been estimated from the low strain rate, Newtonian, shear viscosity, using the Maxwell relationship &tgr;=&eegr;S/Gx. Non-Newtonian shear viscosity is observed at strain rates (ϵ=time-1) equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time. Brittle failure of the fibers occurs 2 log10 units of time above the relaxation time. This study illustrates that the occurrence of non-Newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate. High-silica rhyolite melts involved in ash flow eruptions are expected to undergo a non-Newtonian phase of a deformation immediately prior to brittle failure. ¿American Geophysical Union 1990

BACKGROUND DATA FILES

Abstract

Keywords
Tectonophysics, Rheology—general, Mineralogy and Petrology, Igneous petrology, Physical Properties of Rocks, Fracture and flow
Journal
Journal of Geophysical Research
http://www.agu.org/journals/jb/
Publisher
American Geophysical Union
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