Geo-Marine Letters

, Volume 20, Issue 1, pp 10-19

Gas and fluid venting at the Makran accretionary wedge off Pakistan

  • U. von RadAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
  • , U. BernerAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
  • , G. DelisleAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
  • , H. Doose-RolinskiAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
  • , N. FechnerAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
  • , P. LinkeAffiliated withGEOMAR, Wischhofstr. 1–3, 24148 Kiel, Germany
  • , A. LückgeAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
  • , H. A. RoeserAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
  • , R. SchmaljohannAffiliated withInstitut für Meereskunde, Düsternbrooker Weg 20, 24105 Kiel, Germany
    • , M. WiedickeAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany e-mail: U.vonRad@bgr.de
    • ,  SONNE 122/130 Scientific PartiesAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , M. BlockAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , V. DammAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , J. ErbacherAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , J. FritschAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , B. HarazimAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , J. PoggenburgAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , G. ScheederAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , B. SchreckenbergerAffiliated withBGR, P.O. Box 510153, 30631 Hannover, Germany
    • , N. von MirbachAffiliated withGEOMAR, Wischhofstr. 1–3, 24148 Kiel, Germany
    • , M. DrewsAffiliated withInstitut für Meereskunde, Düsternbrooker Weg 20, 24105 Kiel, Germany
    • , S. WalterAffiliated withInstitut für Meereskunde, Düsternbrooker Weg 20, 24105 Kiel, Germany
    • , A. Ali KhanAffiliated withNational Institute of Oceanography, 47 S.T., Karachi, Pakistan
    • , A. InamAffiliated withNational Institute of Oceanography, 47 S.T., Karachi, Pakistan
    • , M. TahirAffiliated withNational Institute of Oceanography, 47 S.T., Karachi, Pakistan
    • , A. R. TabrezAffiliated withNational Institute of Oceanography, 47 S.T., Karachi, Pakistan
    • , A. H. CheemaAffiliated withHydrocarbon Development Institute of Pakistan, P.O. Box 1308, Islamabad, Pakistan
    • , M. PervazAffiliated withHydrocarbon Development Institute of Pakistan, P.O. Box 1308, Islamabad, Pakistan
    • , M. AshrafAffiliated withOffice of Deputy Hydrographer of Pakistan Navy, 11 Liaquat Barracks, Karachi, Pakistan

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

Abstract

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.