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

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 18 O, and depletion of 2 H 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 × 10 7 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.

Gas Hydrate Accumulation and Occurrence Associated with Cold Seep Systems in the Northern South China Sea: An Overview

“…In addition, geochemical studies of the hydrocarbons collected from the mud volcano development area show that the δ 13 values range from -103‰ to -35.6‰, and most of the values are greater than -50‰, indicating that the hydrate gases are a mixture of biogenic and thermogenic gases, with a bias toward thermogenic gas. This also indicates the contribution of deep mature source rocks to the gas hydrate accumulation [130,144].…”

Fluid seepage on and offshore Western Greece

“…Several different types of fluids that escape from the seabed have been surveyed and studied: (i) hydrothermal fluids (e.g., Tao et al, 2020); (ii) geological hydrocarbon, methane-rich gas of microbial, thermogenic or mixed (e.g., Thiagarajan et al, 2020) and abiotic origin (Sciarra et al, 2019); (iii) modern microbial (e.g., Deville et al, 2020); (iii) freshwater discharges (Christodoulou et al, 2003;Whiticar, 2002); (iv) porewater escape (Harrington, 1985); (v) gas and oil saturated water and mud discharges from mud volcanoes (e.g., Chen et al, 2020).…”

“…Methane seeps have been discovered in continental shelves, the deep ocean-floor, the intervening slope , in in open and semi-enclosed shallow gulfs and lagoons (Hasiotis et al, 1996, Rogers et al, 2006, in midlatitude estuaries (called rias in the Iberian margin) (Garcia-Garcia et al, 1999;Ussler et al, 2003), and even at the deepest part of the ocean; the Marianna Trench (Kojima and Watanabe, 2015). Natural gas and other related fluids accumulations on the marine sediments may alter locally the morphology of the seabed, forming features like submarine mud volcanoes (Chen et al, 2020;Pierre et al, 2014;Neurauter and Roberts, 1994;Milkov, 2000), carbonate mounds (Roberts and Ballard, 2001;Roberts et al, 1990) and pockmarks (e.g., Gullapalli et al, 2019;Christodoulou et al, 2009;Whiticar, 2002;Hasiotis et al, 1996;. Gas hydrates are icelike crystalline solids (Milkov, 2000).…”

“…MBES have been extensively used for seabed fluid flow surveying, such as detection and localization of bubble plumes/gas flares (Chen et al, 2020;Idczak et al, 2020) and gas flux estimation (Leifer et al, 2017).…”

“…MBES have been vastly used for the detection, mapping and study of fluid seepage related morphological expressions (Judd and Hovland, 1992), such as pockmarks (Davy et al, 2010;Idczak et al, 2020;Coskun et al, 2016), mud volcanoes (Isola et al, 2020;Chen et al, 2020), methane hydrate mounds (Liu, 2017;Greinert et al, 2010), and carbonate mounds .…”