Gas and fluid venting at the Makran Accretionary Wedge off Pakistan

von Rad, U., Berner, U., Delisle, G., Doose-Rolinski, H., Fechner, N., Linke, Peter, Lückge, A., Roeser, H. A., Schmaljohann, Rolf and Wiedicke, M. and SONNE 122/130 Scientific Parties (2000) Gas and fluid venting at the Makran Accretionary Wedge off Pakistan Geo-Marine Letters, 20 . pp. 10-19. DOI 10.1007/s003670000033.

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The Makran accretionary complex shows a distinct bottom-simulating reflector, indicating a thick gas-hydrate-bearing horizon between the deformational front and about 1350 m water depth which seals off the upward flow of gas-charged fluids. A field of presently inactive mud diapirs with elevations up to 65 m was discovered in the abyssal plain seawards of the deformation front, suggesting that in the past conditions were favorable for periodic but localized vigorous mud diapirism. Regional destabilization of the gas hydrate leading to focused flow was observed where deep-penetrating, active faults reach the base of the gas-hydrate layer, as in a deeply incised submarine canyon (2100–2500 m water depth). At this location we discovered seeps of methane and H2S-rich fluids associated with chemoautotrophic vent faunas (e.g., Calyptogena sp.). Driven by the accretionary wedge dynamics, the landward part of the gas-hydrate layer below the Makran margin is being progressively uplifted. Due to reduced hydrostatic pressure and rising ocean bottom-water temperatures, gas hydrates are progressively destabilized and dissociated into hydrate water, methane and H2S. Sediment temperatures lie outside the methane stability field wherever water depth is less than 800 m. Above this depth, upward migration of fluids to the seafloor is unimpeded, thus explaining the abundance of randomly distributed gas seeps observed at water depths of 350 to 800 m.

Document Type: Article
Keywords: Makran accretionary wedge, Pakistan, gas hydrates
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB3 Marine Ecology > FB3-MI Marine Microbiology
Refereed: Yes
DOI etc.: 10.1007/s003670000033
ISSN: 0276-0460
Date Deposited: 18 Feb 2008 17:24
Last Modified: 19 Jan 2018 11:53

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