Physics-controlled thickness of shear zones caused by viscous heating: Implications for crustal shear localization

We evaluate the parameters that control the thickness of ductile shear zones that are generated by viscous heating. We employ two-dimensional thermomechanical numerical models to simulate shear zone development under compression. Results show that the shear zone thickness is essentially independent on the numerical resolution and the initial size of a weak inclusion that triggers shear localization. A simple scaling law is derived which predicts the thickness with six physical parameters: far-field stress and strain rate, thermal conductivity (both constant and temperature dependent), initial temperature, activation energy, and stress exponent. The scaling law is confirmed by numerical simulations for a wide range of parameters. For crustal deformation conditions typical temperature increase ranges between 50◦C and 200◦C, and the predicted thickness is between 1 km and 7 km. These thicknesses agree with natural crustal and lithospheric shear zones suggesting that shear heating is a process controlling crustal shear zone formation.