Mantle-derived helium released through the Japan trench bend-faults

Mantle-derived helium released through the Japan trench bend-faults

Blog Article

Abstract Plate bending-related normal faults (i.e.bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction here zone.

Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate.However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect.This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across pure energy jeans the outer slope of the Japan trench.

The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow.Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.