Transient Creep of Quartz and Granulite at High Temperature Under Wet Conditions

Abstract

Transient creep of crustal rocks is important to explain time‐dependent geological processes such as postseismic deformation following a large continental earthquake. While the steady‐state creep flow law parameters of quartz and feldspar, major minerals in the upper and lower crust, are well known, the physical mechanism behind transient creep and the corresponding flow law parameters are poorly understood. We quantify the flow law parameters for both quartz and granulite (mixture of plagioclase and pyroxene) under wet conditions with a nonlinear Burgers model using a Markov chain Monte Carlo (MCMC) method. Modeling results yield an activation energy of 70 ± 20 kJ/mol and a stress exponent of 2.0 ± 0.1 for transient creep of quartz aggregates. For granulite/feldspar, we find activation energies of 280 ± 30 and 220 ± 20 kJ/mol and stress exponents of 1.0 ± 0.2 and 0.9 ± 0.1 under mid (1050–1100°C) and high (1125–1150°C), temperature conditions, respectively. The stress exponents and activation energies of transient creep are consistently smaller than those of steady‐state creep for both quartz and granulite/feldspar. Combined with results for transient creep of olivine that were previously obtained (Masuti & Barbot, 2021, https://doi.org/10.1186/s40623-021-01543-9), we suggest that the activation energies and stress exponents of transient creep are smaller than those of steady‐state creep for volumetrically important silicate minerals of the crust and upper mantle. Extrapolation of the estimated flow law parameters of granulite/feldspar to natural conditions suggests that transient creep may dominate during the postseismic period and lasts longer than previously thought.