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Natural and Experimental Constraints on a Flow Law for Dislocation‐Dominated Creep in Wet Quartz
Author(s) -
Lusk Alexander D. J.,
Platt John P.,
Platt Jason A.
Publication year - 2021
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2020jb021302
Subject(s) - creep , quartz , rheology , dislocation creep , dislocation , deformation (meteorology) , overburden pressure , differential stress , materials science , geology , law , thermodynamics , physics , composite material , geotechnical engineering , political science
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:ε ˙ = Aσ nf H 2 O re −( Q + V P)/ 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 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.