Episodic Slow Slip Hosted by Talc-Bearing Metasomatic Rocks: High Strain Rates and Stress Amplification in a Chemically Reacting Shear Zone

Episodic tremor and slow slip (ETS) downdip of the subduction seismogenic zone are poorly understood slip behaviors of the seismic cycle. Talc, a common metasomatic mineral at the subduction interface, is suggested to host slow slip but this hypothesis has not been tested in the rock record. We investigate actinolite microstructures from talc-bearing and talc-free rocks exhumed from the depths of modern ETS (Pimu'nga/Santa Catalina Island, California). Actinolite deformed by dissolution-reprecipitation creep in the talc-free rock and dislocation creep +/- cataclasis in the talc-bearing rock. This contrast results from stress amplification in the talc-bearing rock produced by high strain rates in surrounding weak talc. We hypothesize that higher strain rates in the talc-bearing sample represent episodic slow slip, while lower strain rates in the talc-free sample represent intervening aseismic creep. This work highlights the need to consider fluid-mediated chemical change in studies of subduction zone deformation and seismicity.