Strong Serpentinization and Hydration in the Subducting Plate of the Southern Mariana Trench: Insights From Vp/Vs Ratios

Abstract

The southern Mariana subduction zone, home to the Challenger Deep—the deepest known point on Earth—poses significant challenges for studying the hydration of the subducting plate due to its extreme depth. This study uses S-wave seismic tomography and V_p/V_s ratios to investigate hydration and serpentinization at the Challenger Deep. We observe a low V_p and V_s layer in the upper mantle with V_p/V_s ratios exceeding 1.8, reaching up to 1.95 at the Moho. These high ratios indicate a strong serpentinized layer (>15 vol%) with significant changes in the mechanical properties of the serpentinized peridotite. Additionally, V_p/V_s ratios in the crust and uppermost mantle increase from the outer rise to the trench axis, demonstrating that bending-related faulting and hydration intensify as the plate approaches the trench. Our results suggest extensive faulting, hydration, and mantle serpentinization at the Challenger Deep, making this region an extreme example of water cycling in subduction zones.