Subducting volcaniclastic-rich upper crust supplies fluids for shallow megathrust and slow slip

Recurring slow slip along near-trench megathrust faults occurs at many subduction zones, but for unknown reasons, this process is not universal. Fluid overpressures are implicated in encouraging slow slip; however, links between slow slip, fluid content, and hydrogeology remain poorly known in natural systems. Three-dimensional seismic imaging and ocean drilling at the Hikurangi margin reveal a widespread and previously unknown fluid reservoir within the extensively hydrated (up to 47 vol % H2O) volcanic upper crust of the subducting Hikurangi Plateau large igneous province. This similar to 1.5 km thick volcaniclastic upper crust readily dewaters with subduction but retains half of its fluid content upon reaching regions with well-characterized slow slip. We suggest that volcaniclastic-rich upper crust at volcanic plateaus and seamounts is a major source of water that contributes to the fluid budget in subduction zones and may drive fluid overpressures along the megathrust that give rise to frequent shallow slow slip.

Automated summary

This article investigates the relationship between slow slip, fluid content, and hydrogeology in subduction zones. Through seismic imaging and ocean drilling, a widespread and previously unknown fluid reservoir was discovered at the Hikurangi margin. The research suggests that the volcaniclastic-rich upper crust at volcanic plateaus and seamounts is a major source of water that contributes to fluid budgets in subduction zones and may drive fluid overpressures along the megathrust that give rise to frequent shallow slow slip.