Natural and Experimental Constraints on a Flow Law for Dislocation-Dominated Creep in Wet Quartz

We present a flow law for dislocation-dominated creep in wet quartz derived from compiled experimental and field-based rheological data. By integrating the field-based data, including independently calculated strain rates, deformation temperatures, pressures, and differential stresses, we add constraints for dislocation-dominated creep at conditions unattainable in quartz deformation experiments. A Markov Chain Monte Carlo (MCMC) statistical analysis computes internally consistent parameters for the generalized flow law: epsilon = A sigma(n)fH2Ore(-(Q+VP)/RT). From this initial analysis, we identify different effective stress exponents for quartz deformed at confining pressures above and below similar to 700 MPa. To minimize the possible effect of confining pressure, compiled data are separated into low-pressure (<560 MPa) and high-pressure (700-1,600 MPa) groups and reanalyzed using the MCMC approach. The low-pressure data set, which is most applicable at midcrustal to lower-crustal confining pressures, yields the following parameters: log(A) = -9.30 +/- 0.66 MPa-n-r s(-1); n = 3.5 +/- 0.2; r = 0.49 +/- 0.13; Q = 118 +/- 5 kJ mol(-1); and V = 2.59 +/- 2.45 cm(3) mol(-1). The high-pressure data set produces a different set of parameters: log(A) = -7.90 +/- 0.34 MPa-n-r s(-1); n = 2.0 +/- 0.1; r = 0.49 +/- 0.13; Q = 77 +/- 8 kJ mol(-1); and V = 2.59 +/- 2.45 cm(3) mol(-1). Predicted quartz rheology is compared to other flow laws for dislocation creep; the calibrations presented in this study predict faster strain rates under geological conditions by more than 1 order of magnitude. The change in n at high confining pressure may result from an increase in the activity of grain size sensitive creep.

Automated summary

A flow law for dislocation-dominated creep in wet quartz was derived from compiled experimental and field-based rheological data. Through statistical analysis, internally consistent parameters were computed. The study revealed different effective stress exponents for quartz deformed at high and low confining pressures, possibly due to increased activity of grain size sensitive creep.