Borehole observations of fluid flow from South Chamorro Seamount, an active serpentinite mud volcano in the Mariana forearc

C. Geoffrey Wheat, Patricia Fryer, Andrew T. Fisher, Samuel Hulme, Hans Jannasch, Michael J. Mottl, Keir Becker

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

A sealed borehole observatory (CORK) was deployed on South Chamorro Seamount, an active serpentinite mud volcano in the Mariana forearc to explore subduction-related processes on a non-accretionary, convergent plate margin. Formation fluid was overpressured relative to ambient hydrostatic conditions. Fluid flowed from the borehole at ~ 0.2 L/s when the observatory was opened to recover instruments 2 yr after it was installed. The chemical composition of the formation fluid is similar to that extrapolated from trends in pore water data collected during Ocean Drilling Program Leg 195 when the observatory was established. Reduced sulfur is present in this highly-alkaline (pH 12.4) formation fluid, indicative of microbial activity at or below the depth of the screened casing, 149-202 m below the seafloor. Discharge from the open borehole continued for 37 days, until the observatory was resealed. This discharge requires significant permeability at depth (> 6 × 10- 14 m2). Zones of high permeability may be associated with the formation of headwall scarps, consistent with numerous slumps on the southeastern flank of the seamount, and likely shape a geochemical environment suitable for an active microbial community.

Original languageEnglish (US)
Pages (from-to)401-409
Number of pages9
JournalEarth and Planetary Science Letters
Volume267
Issue number3-4
DOIs
StatePublished - Mar 30 2008

Keywords

  • CORK
  • Mariana forearc
  • marine hydrogeology
  • mud volcano
  • serpentinite
  • subduction

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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