Reversible water weakening of quartz
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abstract
We have performed looped pressure-stepping deformation experiments at the same temperature (800C) and strain rate (210-6s-1) on a milky quartz crystal and a quartzite that deform by dislocation creep. Our results demonstrate that flow strengths at fixed water content depend on fH2O, and that the dependence is reversible. Thus, rheology of quartzite can be predicted if fH2O is known. In addition, the effect of fH2O on strength of quartzite is greater than that of the milky quartz single crystal. The differing sensitivities are due to differing effects that water has on deformation and recovery within grain interiors and at (or near) grain boundaries. These results indicate that, as temperature increases with depth and the dominant recovery mechanism of dislocation creep changes from recrystallization at grain boundaries to intragranular recovery, dependence of quartz creep on fH2O may also decrease. 2013 Elsevier B.V.