An evaluation of quartzite flow laws based on comparisons between experimentally and naturally deformed rocks

We use the remarkable similarity between microstructures preserved in natur ally and experimentally deformed quartzites as a basis to evaluate quartzit e flow laws and their application to natural conditions. The precision of t his analysis is relatively high because of the well-constrained deformation history of naturally deformed rocks from the Ruby Gap duplex, Central Aust ralia. The external state variables during deformation in the duplex are we ll constrained by a combination of thermochronological, microstructural and structural observations. Using a flow law with the form epsilon over dot = Af(H2O)(m)sigma (n) exp(-Q/RT), our analysis indicates that values of log (A)=-11.2 +/-0.6 MPa-n/s and Q=135 +/- 15 kJ/mol provide the best descripti on 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 in fluence of water fugacity on strain rate determined in the laboratory In th is case, we concur with a previously published suggestion that the measured effect of water fugacity (epsilon over dot proportional to f(H2O)(2)) is l ikely a manifestation of a change in deformation process with increasing st ress. 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 deform ation microstructures in naturally deformed rocks.