We use the remarkable similarity between microstructures preserved in naturally and experimentally deformed quartzites as a basis to evaluate quartzite flow laws and their application to natural conditions. The precision of this analysis is relatively high because of the well-constrained deformation history of naturally deformed rocks from the Ruby Gap duplex, Central Australia. The external state variables during deformation in the duplex are well constrained by a combination of thermochronological, microstructural and structural observations. Using a flow law with the form _ e Af m H 2 O s n exp ÀQ=RT , our analysis indicates that values of log (A)=±11.20.6 MPa ±n /s and Q=135 15 kJ/mol provide the best description of the combined natural and experimental constraints with values of m=1 and n=4. Motivated by the results of our analysis, we also evaluated the influence of water fugacity on strain rate determined in the laboratory. In this case, we concur with a previously published suggestion that the measured effect of water fugacity (_ e G f 2 H 2 O ) is likely a manifestation of a change in deformation process with increasing stress. The results of this study provide further support for the application of quartzite flow laws to understand deformation conditions in the Earth, and emphasize the important insights that can be gained by analyzing deformation microstructures in naturally deformed rocks.

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