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 ε = AfmH2Oσn 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 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 (ε∝ f2H2O) 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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Acknowledgements The results of this study were originally presented at the Rheology and Deformation Mechanism conference held in Basel in 1997. We thank both the convenors of that conference (S. Schmid, R. Heilbronner, and H. Stünitz) and the convenors of the conference in Neustadt (G. Dresen and M. Handy) for continuing a great tradition. We are also grateful for the numerous great conversations we have had with Jan Tullis on the rheology of quartzite. This paper would never have been written without the work she and her students and colleagues have done over the years. We would also like to thank Renee Heilbronner, Holger Stünitz and Michael Stipp for many helpful discussions during the final stages of development of this project, and Bernhard Stöckhert and Chris Spiers for thoughtful reviews of the submitted manuscript. Greg Hirth was funded by NSF grant EAR-9726125 and the Keck Geodynamics program at WHOI. We also offer a belated thank you to Ann Mulligan for her help in collecting samples in the Ruby Gap duplex.
- Flow laws
- Quartzite Recrystallization