Geological Records of Transient Fluid Drainage into the Shallow Mantle Wedge

Pore fluid pressure on subduction zone megathrusts is lowered by fluid drainage into the overlying plate, af-fecting subduction zone seismicity. However, the spatial and temporal scales of fluid flow through suprasub-duction zones are poorly understood. We constrain the duration and velocity of fluid flow through a shallow mantle wedge based on the analyses of vein networks consisting of high-temperature serpentine in hydrated ultramafic rocks from the Oman ophiolite. On the basis of a diffusion model and the time-integrated fluid flux, we show that the channelized fluid flow was short-lived (2.1 x 10-1 to 1.1 x 101 years) and had a high fluid velocity (2.7 x 10-3 to 4.9 x 10-2 meters second-1), which is close to the propagation velocities of seismic events in present-day subduction zones. Our results suggest that the drainage of fluid into the overlying plate occurs as episodic pulses, which may influence the recurrence of megathrust earthquakes.