Hydrocarbon seepage and its sources at mud volcanoes of the Kumano forearc basin, Nankai Trough subduction zone

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doi: 10.1002/2013GC005057
Author(s): Pape, Thomas; Geprägs, Patrizia; Hammerschmidt, Sebastian; Wintersteller, Paul; Wei, Jiangong; Fleischmann, Timo; Bohrmann, Gerhard; Kopf, Achim J.
Author Affiliation(s): Primary:
University of Bremen, Center for Marine Environmental Sciences, Bremen, Germany
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 15(6), p.2180-2194. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English; illus., incl. 3 tables, sketch map
Summary: Twelve submarine mud volcanoes (MV) in the Kumano forearc basin within the Nankai Trough subduction zone were investigated for hydrocarbon origins and fluid dynamics. Gas hydrates diagnostic for methane concentrations exceeding solubilities were recovered from MVs 2, 4, 5, and 10. Molecular ratios (C1/C2 < 250) and stable carbon isotopic compositions (δ13C-CH4 >-40 ppm V-PDB) indicate that hydrate-bound hydrocarbons (HCs) at MVs 2, 4, and 10 are derived from thermal cracking of organic matter. Considering thermal gradients at the nearby IODP Sites C0009 and C0002, the likely formation depth of such HCs ranges between 2300 and 4300 m below seafloor (mbsf). With respect to basin sediment thickness and the minimum distance to the top of the plate boundary thrust we propose that the majority of HCs fueling the MVs is derived from sediments of the Cretaceous to Tertiary Shimanto belt below Pliocene/Pleistocene to recent basin sediments. Considering their sizes and appearances hydrates are suggested to be relicts of higher MV activity in the past, although the sporadic presence of vesicomyid clams at MV 2 showed that fluid migration is sufficient to nourish chemosynthesis-based organisms in places. Distributions of dissolved methane at MVs 3, 4, 5, and 8 pointed at fluid supply through one or few MV conduits and effective methane oxidation in the immediate subsurface. The aged nature of the hydrates suggests that the major portion of methane immediately below the top of the methane-containing sediment interval is fueled by current hydrate dissolution rather than active migration from greater depth. Abstract Copyright (2014), American Geophysical Union. All Rights Reserved.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; 29 Economic Geology, Energy Sources; Accretionary wedges; Aliphatic hydrocarbons; Alkanes; Asia; Bathymetry; Biogenic processes; Bivalvia; C-13/C-12; Carbon; Cenozoic; Chemosynthesis; Cretaceous; Expedition 319; Far East; Gas hydrates; Gas seeps; Hydrocarbons; IODP Site C0002; IODP Site C0009; Integrated Ocean Drilling Program; Invertebrata; Isotope ratios; Isotopes; Japan; Kumano Basin; Mesozoic; Methane; Migration; Mollusca; Mud volcanoes; NanTroSEIZE; Nankai Trough; Natural gas; Neogene; North Pacific; Northwest Pacific; Ocean floors; Organic compounds; Oxidation; Pacific Ocean; Petroleum; Plate boundaries; Plate tectonics; Pleistocene; Pliocene; Quaternary; Seepage; Seismicity; Shimanto Belt; Solution; Stable isotopes; Subduction zones; Tertiary; Thermal properties; West Pacific
Coordinates: N332500 N334500 E1365000 E1362000
Record ID: 2016043623
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom, Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union