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

Abstract

AbstractWe 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: = Aσne−(Q+VP)/RT. From this initial analysis, we identify different effective stress exponents for quartz deformed at confining pressures above and below ∼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 cm3 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 cm3 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.