Discharge of deeply rooted fluids from submarine mud volcanism in the Taiwan accretionary prism
Nai‐Chen ChenTsanyao Frank YangWei‐Li HongTsai‐Luen YuIn‐Tian LinPei‐Ling WangSaulwood LinChih‐Chieh SuChuan‐Chou ShenYunshuen WangLi‐Hung Lin
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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.Keywords:
Seafloor Spreading
Accretionary wedge
Biogeochemical Cycle
Mud volcano
Accretionary wedge
Mud volcano
Abyssal plain
Neogene
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Mineralogical, petrographic and stable isotope analyses were carried out on sediment and rock samples collected from a deep-sea cold seep province in the Paola Ridge (southeastern Tyrrhenian Sea). The results, coupled with the interpretation of the seafloor backscatter, constrained both the biogeochemical zonation and the spatial distribution of the cold seep habitats in the area. These have proved to change in depth in a range of few meters and laterallywithin narrow zones. The mud volcanoes, characterized by a high backscatter signature, are the site of vigorous gas venting and, in the subsurface, show a rapid transition from the oxic sea water interface toward the methane-sulfate transition zone in the sediments. Intermediate backscatter typifies areas where free venting is hampered by the presence of mudflows at the seafloor. These conditions favor: i) the oxidation of sulfides near the seafloor, ii) the precipitation of siderites a few meters below the seafloor and iii) the formation of sulfides deeper in the sub-seafloor. Faults are likely candidates to act as conduits for sulfates and metal oxides that juxtapose different redox environments. Siderites precipitated in the fast and low venting sites showed enrichment in δ13C and δ18O, which are compatible with their precipitation in the methanogenic zone. The heavy-oxygen isotopic compositions of the siderites are possibly related to the dissociation of gas hydrates, which have not been mapped so far by seismic data in the study area. Mud diapirism is characterized by low backscatter seafloor, large fields of pockmarks and is dissected bynormal faults. In coincidence with the normal faults, authigenic calcites and aragonites are present at or very close to the seafloor. They have the typical isotopic signature indicating formation during sulfate-dependent microbially-mediated anaerobic oxidation of methane.They are associated with Lucinoma borealis, the youngest being dated 640-440 BP. This suggests that the seepage activity in the mud diapirs was likely clogged by either carbonates or activity of the faults only very recently.
Seafloor Spreading
Mud volcano
Authigenic
Cold seep
Clathrate hydrate
Isotopic signature
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Accretionary wedge
Mud volcano
Breccia
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Abstract Submarine mud volcanoes are important sources of methane to the water column. However, the temporal variability of their mud and methane emissions is unknown. Methane emissions were previously proposed to result from a dynamic equilibrium between upward migration and consumption at the seabed by methane-consuming microbes. Here we show non-steady-state situations of vigorous mud movement that are revealed through variations in fluid flow, seabed temperature and seafloor bathymetry. Time series data for pressure, temperature, pH and seafloor photography were collected over 431 days using a benthic observatory at the active Håkon Mosby Mud Volcano. We documented 25 pulses of hot subsurface fluids, accompanied by eruptions that changed the landscape of the mud volcano. Four major events triggered rapid sediment uplift of more than a metre in height, substantial lateral flow of muds at average velocities of 0.4 m per day, and significant emissions of methane and CO 2 from the seafloor.
Mud volcano
Seafloor Spreading
Seabed
Clathrate hydrate
Submarine volcano
Submarine landslide
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Mud volcano
Accretionary wedge
Anticline
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Seafloor Spreading
Mud volcano
Seabed
Reflection
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