Short-lived mud volcanism and cold seeps caused by dissociation of gas hydrates in Lake Baikal
Van Rensbergen, P.; De Batist, M.; Klerkx, J.; Poort, J.; Hus, R.; Vanneste, M.; Granin, N.; Krinitsky, P. (2001). Short-lived mud volcanism and cold seeps caused by dissociation of gas hydrates in Lake Baikal. J. Conf. Abstr. 6: 151 In: Journal of Conference Abstracts. Cambridge Publications: Cambridge. ISSN 1362-0886, more |
| Available in | Authors | | Document type: Summary
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| Authors | | Top | - Van Rensbergen, P., more
- De Batist, M., more
- Klerkx, J.
- Poort, J., more
| - Hus, R.
- Vanneste, M., more
- Granin, N.
- Krinitsky, P.
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| Abstract | Four cold seeps are studied in Lake Baikal’s South Basin using side scan sonar in combination with detailed bathymetry, measurements of near-bottom water properties, and selected seismic profiles. The cold seeps occur at the crest of a fault block in the hanging wall of a large normal fault (the Posolsky fault), at a waterdepth of 1340 m to 1420 m. They were named Bolshoy (large), Stari (old), Malenki (small), and Malyutka (very small). The seeps at the lake floor are identified on side scan sonar and echosounding data and interpreted as flat-topped (craters, e.g. Malenki) and/or conical-shaped mud volcanoes (e.g. Bolshoy). Each vent is characterized by a near-bottom acoustic anomaly in the water column. Measurements of near-bottom water properties indicate a negative oxygen anomaly and a small but consistent positive temperature anomaly but no difference in salinity. The expelled fluids appear to be not much different from the lake water and most likely originate from shallow depth, probably from gas hydrate dissociation between 300 m and 150 m below the lake floor.Combination with subsurface data from seismic profiles shows that the seeps occur where the base of gas hydrate layer (BGH) is irregular and shallowing rapidly towards the vent sites. Coincident with the shallowing BGH, positive heat flow anomalies occur. Local dissociation of gas hydrates from the base to the top is attributed to a pulse of hydrothermal heat flow along an active fault segment. Volumetric expansion associated to hydrate dissociation probably caused a high-pressure compartment bounded at the top by the elevated BGH. From the top of the domeshaped BGH a vertical feeder pipe extends to the mud volcano at the lake floor, disrupting the horizontally stratified seismic facies. The mud volcanism seems to be shortlived, as is illustrated by the Bolshoy mud volcano that seems to be in a final phase of mud extrusion despite its recent initiation. The mud volcanoes and cold seeps are interpreted to be an example of a vigorous gas and fluid expulsion caused by gas hydrate dissociation due to a hydrothermal event. The duration of fluid and mud expulsion is limited by the amount of hydrate, by the duration of the hydrothermal pulse, or by the time needed for a new equilibrium to be installed. This mechanism may be an explanation for traces of short-lived mud volcanism in other gas hydrate areas in a tectonically active setting. |
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