Brown, K. M. et al. (1996): The nature, distribution, and origin of gas hydrate in the Chile triple junction region

ODP 141

Brown, K. M.
Scripps Institution of Oceanography, La Jolla, CA, United States

Bangs, N. L.
University of Texas at Austin, Austin, TX, United States

Froelich, P. N.
Georgia Institute of Technology, Atlanta, GA, United States

Kvenvolden, K. A.
U. S. Geological Survey, Menlo Park, CA, United States

The nature, distribution, and origin of gas hydrate in the Chile triple junction region
In: Kastner, Miriam (editor), Seismic indications of gas hydrates in continental margins
Elsevier, Amsterdam, Netherlands
A bottom simulating reflector (BSR) is regionally distributed throughout much of the Chile Triple Junction (CTJ) region. Downhole temperature and logging data collected during Ocean Drilling Program (ODP) Leg 141 suggest that the seismic BSR is generated by low seismic velocities associated with the presence of a few percent free gas in a approximately 10 m thick zone just beneath the hydrate-bearing zone. The data also indicate that the temperature and pressure at the BSR best corresponds to the seawater/methane hydrate stability field. The origin of the large amounts of methane required to generate the hydrates is, however, problematic. Low total organic carbon contents and low alkalinities argue against significant in situ biogenic methanogenesis, but additional input from thermogenic sources also appears to be precluded. Increasing thermal gradients, associated with the approach of the spreading ridge system, may have caused the base of the hydrate stability field to migrate 300 m upwards in the sediments. We propose that the upward migration of the base of the stability field has concentrated originally widely dispersed hydrate patches into the more continuous hydrate body we see today. The methane can be concentrated if the gas hydrates can form from dissolved methane, transported into the hydrate zone via diffusion or fluid advection. A strong gradient may exist in dissolved methane concentration across the BSR leading to the steady reabsorbtion of the free gas zone during the upward migration of the BSR even in the absence of fluid advection.
Coverage:Geographic coordinates:
West:-75.5120East: -75.4120

Oceanography; Applied geophysics; Solid-earth geophysics; bottom simulating reflectors; Chile; Chile Margin Triple Junction; continental margin; downhole methods; East Pacific; electrical methods; gas hydrates; geophysical methods; geophysical profiles; geophysical surveys; heat flow; Leg 141; marine sediments; Ocean Drilling Program; Pacific Ocean; plate tectonics; resistivity; sediments; seismic logging; South America; South Pacific; Southeast Pacific; surveys; temperature logging; triple junctions; well-logging;