Deformation of a metasomatized subduction interface at the depths of episodic tremor and slip
Will Hoover, University of Washington
Cailey Condit, University of Washington
Abstract
Episodic tremor and slow slip (ETS) downdip of the subduction seismogenic zone are poorly understood slip behaviors of the seismic cycle that are thought to occur at the subduction interface. Free fluid, high pore pressures and abundant chemical reactions in this interface produce new lithologies that modify its rheology, but their deformation remains poorly characterized. We investigate a block-in-matrix subduction interface shear zone deformed at the depths of modern ETS (Pimu'nga/Santa Catalina Island, California) to constrain the complex rheology of its talc-, chlorite-, and amphibole-rich metasomatic matrix. Within the matrix alone, multi-scale clast-in-matrix textures, overprinting deformation fabrics, and megablastic fluid pathways suggest time-dependent and complex rheologic contrasts. Quantitative amphibole microstructures record multiple deformation mechanisms modulated by associated mineralogy, rock texture, fluid pressure, and strain rate. First order microstructural contrasts between talc-bearing and talc-free lithologies suggest talc-rich rocks hosted high strain rate deformation consistent with slow slip events. These results provide the most detailed picture to-date of the deformation of metasomatic rocks common in deep subduction interfaces and demonstrate the need to consider fluid-mediated chemical change in studies of subduction zone deformation and seismicity.
Session
Subduction zone geology