Models of quartz overgrowth and vein formation: deformation and episodic fluid flow in an ancient subduction zone

Steady state models of overgrowth and vein formation are developed using kinetic data for quartz dissolution and precipitation and estimates of fluid advection, pore-fluid and grain-boundary diffusion. Application of these models to overgrowths and veins in the Kodiak accretionary complex suggests that the Kodiak Formation deformed continuously by a grain-boundary diffusion-limited mechanism, accompanied by episodic pore fluid diffusion of quartz from the matrix to vertical fluid-filled fractures near the base of the accretionary wedge. A picture emerges of intermittent fluid flow upward from the decollement into a branching hierarchy of vertical fractures in the accretionary wedge during hydrofracturing events, followed by local transport and precipitation of silica causing sealing of the fracture at depth and propagation of pulses of fracture fluid upward. -from Authors