Discharge of deeply rooted fluids from submarine mud volcanism in the Taiwan accretionary prism

Nai-Chen Chen,Tsai-Luen Yu,Chuan-Chou Shen,Yunshuen Wang,Chih-Chieh Su,In-Tian Lin,Wei-Li Hong,Saulwood Lin,Tsanyao Frank Yang,Li-Hung Lin,Pei-Ling Wang

doi:10.1038/s41598-019-57250-9

Abstract

Qualitative and quantitative assessments of fluid cycling are essential to address the role and transport of deeply sourced fluids in subduction systems. In this study, sediment cores distributed across a submarine mud volcano (SMV) offshore southwestern Taiwan were investigated to determine the characteristics of fluids generated through the convergence between the Eurasian and Phillippine Sea Plates. The low dissolved chloride concentration combined with the enrichment of 18O, and depletion of 2H of pore fluids suggest the discharge of deep freshwater formed by smectite dehydration at an equilibrium temperature of 100 to 150 °C. The upward fluid velocities, decreasing from 2.0 to 5.0 cm yr−1 at the center to a negligible value at margin sites, varied with the rate and efficiency of anaerobic methanotrophy, demonstrating the impact of fluid migration on biogeochemical processes and carbon cycling. By extrapolating the velocity pattern, the flux of fluids exported from 13 SMVs into seawater amounted up to 1.3–2.5 × 107 kg yr−1, a quantity accounting for 1.1–28.6% of the smectite-bound water originally stored in the incoming sediments. Our results imply that SMVs could act as a conduit to channel the fluids produced from great depth/temperature into seafloor environments in a subduction system of the western Pacific Ocean.

Highlights

Qualitative and quantitative assessments of fluid cycling are essential to address the role and transport of deeply sourced fluids in subduction systems
The exact characteristics and quantities of deep fluids discharged from submarine mud volcano (SMV), and their impacts on biogeochemical activities remain poorly constrained in the subduction system of the western Pacific Ocean
We present a comprehensive geochemical dataset of fluids extracted from sediment cores recovered from sites distributed across an SMV, TY1, in the accretionary prism offshore southwestern Taiwan (Fig. 1)

Summary

Introduction

While SMVs provide a window to witness the deep subsurface characteristics, upward migrating hydrocarbon gases produced by thermal maturation or methanogenesis drive the sulfate-dependent anaerobic oxidation of methane (AOM) at shallow depths[9,10] Such a biological removal mechanism has been considered to be effective in maintaining a low level of methane in seawater[15]. We present a comprehensive geochemical dataset of fluids extracted from sediment cores recovered from sites distributed across an SMV, TY1, in the accretionary prism offshore southwestern Taiwan (Fig. 1). These data were used to assess the fluid source, formation temperature, and fluid-rock ratio for the reaction in the source region. The possible fluid transport pathways in the Taiwan accretionary prism were discussed

Methods

Results

Discussion

Conclusion