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The nature, distribution, and origin of gas hydrate in the Chile Triple Junction region

Earth and Planetary Science Letters

By:
, , ,
DOI: 10.1016/0012-821X(95)00243-6

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Abstract

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.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The nature, distribution, and origin of gas hydrate in the Chile Triple Junction region
Series title:
Earth and Planetary Science Letters
DOI:
10.1016/0012-821X(95)00243-6
Volume
139
Issue:
3-4
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Earth and Planetary Science Letters
First page:
471
Last page:
483
Number of Pages:
13