The nature, distribution, and origin of gas hydrate in the Chile triple junction region

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doi: 10.1016/0012-821X(95)00243-6
Author(s): Brown, K. M.; Bangs, N. L.; Froelich, P. N.; Kvenvolden, K. A.
Author Affiliation(s): Primary:
Scripps Institution of Oceanography, La Jolla, CA, United States
Other:
University of Texas at Austin, Austin, TX, United States
Georgia Institute of Technology, Atlanta, GA, United States
U. S. Geological Survey, Menlo Park, CA, United States
Volume Title: Seismic indications of gas hydrates in continental margins
Volume Author(s): Kastner, Miriam, editor
Source: Seismic indications of gas hydrates in continental margins, edited by Miriam Kastner. Earth and Planetary Science Letters, 139(3-4), p.471-483. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 40 refs.; illus., incl. sects., sketch map
Summary: 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 ∼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.
Year of Publication: 1996
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; 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
Coordinates: S463040 S455100 W0754120 W0755120
Record ID: 1996047144
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