TY  - JOUR
A1  - Döhmann, Maximilian J.E.A.
A1  - Brune, Sascha
A1  - Nardini, Livia
A1  - Rybacki, Erik
A1  - Dresen, Georg
T1  - Strain Localization and Weakening Processes in Viscously Deforming Rocks
BT  - Numerical Modeling Based on Laboratory Torsion Experiments
JF  - Journal of geophysical research : JGR
N2  - Localization processes in the viscous lower crust generate ductile shear zones over a broad range of scales affecting long‐term lithosphere deformation and the mechanical response of faults during the seismic cycle. Here we use centimeter‐scale numerical models in order to gain detailed insight into the processes involved in strain localization and rheological weakening in viscously deforming rocks. Our 2‐D Cartesian models are benchmarked to high‐temperature and high‐pressure torsion experiments on Carrara marble samples containing a single weak Solnhofen limestone inclusion. The models successfully reproduce bulk stress‐strain transients and final strain distributions observed in the experiments by applying a simple, first‐order softening law that mimics rheological weakening. We find that local stress concentrations forming at the inclusion tips initiate strain localization inside the host matrix. At the tip of the propagating shear zone, weakening occurs within a process zone, which expands with time from the inclusion tips toward the matrix. Rheological weakening is a precondition for shear zone localization, and the width of this shear zone is found to be controlled by the degree of softening. Introducing a second softening step at elevated strain, a high strain layer develops inside the localized shear zone, analogous to the formation of ultramylonite bands in mylonites. These results elucidate the transient evolution of stress and strain rate during inception and maturation of ductile shear zones.
KW  - dislocation creep
KW  - torsion
KW  - 2-D numerical model
KW  - rheological weakening
KW  - two phase aggregates
KW  - strain localization
Y1  - 2018
U6  - https://doi.org/10.1029/2018JB016917
SN  - 0148-0227
SN  - 2169-9356
VL  - 124
IS  - 1
SP  - 1120
EP  - 1137
PB  - Union
CY  - Washington, DC
ER  -