Short-lived subduction interface fluid transport at the depths of episodic tremor and slow slip [dataset]

Abstract

Geophysical observations and geologic evidence suggest the source region of deep episodic tremor and slow slip (ETS) at the subduction interface is fluid rich and subject to high pore fluid pressure, however the mechanistic role of fluid in producing this seismic phenomenon remains debated. Previous studies have linked fluid movement and seismicity through diffusion chronometry, capable of resolving fluid transport durations at timescales comparable to the seismic cycle, but none have directly constrained the timescales of fluid transport at the subduction interface, the inferred source region of ETS. We invert measured Li concentration and isotope profiles using a Monte Carlo Li advection-diffusion model to constrain the duration (and associated uncertainties) of fluid transport around two partially-reacted metamafic blocks from an exhumed subduction interface (Amphibolite Unit, Catalina Schist, California). Both blocks yield time-integrated durations of fluid transport of ~40 years (years to centuries at 95% confidence) much shorter than the lifetime of these rocks in the subduction zone and comparable to, or longer than, the longest slow slip events. This suggests that fluid transport does not occur continuously at the subduction interface but rather reflects transport through fracture permeability consistent with fault-valve type models of fluid transport and related pore pressure fluctuation and frictional instability. The presence of peak metamorphic quartz + garnet veins in the rinds supports the formation and healing of fracture permeability as the process controlling fluid transport at the subduction interface. The fluid transport recorded by these blocks may be the geologic record of geophysically-observed variations in Vp/Vs during the slow slip cycle in modern subduction zones.