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

Jin-Oh Park,Gou Fujie,Asuka Yamaguchi,Naoto Takahata,Makoto Yamano,Juichiro Ashi,Yue Sun,Ehsan Jamali Hondori,Yuji Sano,Takanori Kagoshima,Tetsuro Tsuru

doi:10.1038/s41598-021-91523-6

Abstract

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

Highlights

Plate bending-related normal faults develop at the outer trench-slope of the oceanic plate incoming into the subduction zone
This study reports mantle-derived helium released through the Japan trench bend-faults and propose a hydrothermal circulation through bend-faults across the Moho
At two transects crossing the Japan trench, surface sediments were collected by using gravity corers at six seafloor sites located nearby the bend-faults, and pore-fluids were extracted from the surface sediment samples (Fig. 1, “Methods” section)

Summary

Introduction

Plate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. At two transects crossing the Japan trench, surface sediments were collected by using gravity corers at six seafloor sites located nearby the bend-faults, and pore-fluids were extracted from the surface sediment samples (Fig. 1, “Methods” section).

Results

Conclusion