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Experimental rock deformation is fundamental to our understanding of physical processes that govern the mechanical properties of geomaterials. It generates crucial information, which is also relevant for other areas of geoscience, such as, structural geology, seismology, engineering geology, geodesy, mantle dynamics, planetary dynamics, hydrology, energy resource management, etc. Accordingly, one of the important aspects of rock deformation is to constrain the constitutive equations and flow law parameters of geologically important materials, for example, quartz, feldspar, olivine, pyroxene, etc.
Quartz rheology in the presence of H2O is fundamental to model the deformation behavior of the continental crust. Microstructures in many naturally deformed quartzites in crustal conditions show evidence of crystal-plastic deformation, which is interpreted as the consequence of the grain size insensitive (GSI) creep process. However, earlier experimentally determined flow law parameters of polycrystalline quartz aggregate by different groups show many inconsistencies. In order to constrain a robust creep law for wet quartzite (as-is and 0.1 wt% H2O added), we have generated novel high-resolution data through constant-load coaxial deformation experiments of natural coarse-grained (~ 200 μm) high purity Tana quartzite in a new generation Griggs apparatus. Creep tests were performed at 700 to 900 °C temperature under 1 GPa confining pressure. In contrast to earlier strain-rate stepping experiments, the constant-load procedure needs lower strain at each step to achieve steady-state conditions. Our creep results yield a much lower stress exponent value (n = 1.8 to 2) than the values expected for pure dislocation creep. Microstructural investigations indicate a contribution of diffusion creep.
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