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Marine Geophysical Researches

, Volume 31, Issue 1–2, pp 1–16 | Cite as

Characterizing the thermal regime of cold vents at the northern Cascadia margin from bottom-simulating reflector distributions, heat-probe measurements and borehole temperature data

  • M. Riedel
  • A. M. Tréhu
  • G. D. Spence
Original Research Paper

Abstract

Several cold vents are observed at the northern Cascadia margin offshore Vancouver Island in a 10 km2 region around Integrated Ocean Drilling Program Expedition 311 Site U1328. All vents are linked to fault systems that provide pathways for upward migrating fluids and at three vents methane plumes were detected acoustically in the water column. Downhole temperature measurements at Site U1328 revealed a geothermal gradient of 0.056 ± 0.004°C/m. With the measured in situ pore-water salinities the base of methane hydrate stability is predicted at 218–245 meters below seafloor. Heat-probe measurements conducted across Site U1328 and other nearby vents showed an average thermal gradient of 0.054 ± 0.004°C/m. Assuming that the bottom-simulating reflector (BSR) marks the base of the gas hydrate stability zone variations in BSR depths were used to investigate the linkages between the base of the gas hydrate stability zone and fluid migration. Variations in BSR depth can be attributed to lithology-related velocity changes or variations of in situ pore-fluid compositions. Prominent BSR depressions and reduced heat flow are seen below topographic highs, but only a portion of the heat flow reduction can be due to topography-linked cooling. More than half of the reduction may be due to thrust faulting or to pore-water freshening. Distinct changes in BSR depth below seafloor are observed at all cold vents studied and some portion of the observed decrease in the BSR depth was attributed to fault-related upwelling of warmer fluids. The observed decrease in BSR depth below seafloor underneath the vents ranges between 7 and 24 m (equivalent to temperature shifts of 0.07–0.15°C).

Keywords

Gas hydrate Bottom-simulating reflector IODP Borehole studies Heat flow Fault controlled fluid flow Variations in BSR depth 

Notes

Acknowledgments

We thank the Integrated Ocean Drilling Program (IODP), the National Science Foundation, and The US Department of Energy, National Gas Hydrate Research Program for making this research possible. We acknowledge the contribution of the shipboard party of IODP Expedition 311. The authors would further like to acknowledge the contributions of the Coast Guard crews onboard the research vessel John P. Tully and scientists involved in the data acquisition of the seismic data sets. Furthermore the author wants to acknowledge Seismic Micro Technology for the use of Kingdom Suite.

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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  1. 1.Natural Resources CanadaGeological Survey of Canada, Pacific, Sidney SubdivisionSidneyCanada
  2. 2.College of Oceanic and Atmospheric SciencesOregon State UniversityCorvallisUSA
  3. 3.School of Earth and Ocean SciencesUniversity of VictoriaVictoriaCanada

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