Geochemische Untersuchungen an hydrothermal beeinflußten Sedimenten der Bransfield Straße
This work presents investigations of hydrothermally influenced sediments of the Bransfield Strait, an extensional marginal basin between the Antarctic Peninsula and the South Shetland lslands. Although the hydrothermal activity of Bransfield Strait has been documented since the mid-eighties, the fir...
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| Format: | Thesis |
| Language: | German |
| Published: |
2000
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| Online Access: | https://oceanrep.geomar.de/id/eprint/58862/ https://oceanrep.geomar.de/id/eprint/58862/1/Diss_D%C3%A4hlmann_A_2000.pdf |
| Summary: | This work presents investigations of hydrothermally influenced sediments of the Bransfield Strait, an extensional marginal basin between the Antarctic Peninsula and the South Shetland lslands. Although the hydrothermal activity of Bransfield Strait has been documented since the mid-eighties, the first samples of warm, hydrothermally influenced sediments at Hook Ridge were obtained during the expeditions ANT-XV/2 with RN Polarstern in 1997/98 and NBP 99-04 with RN IB N. B.Palmer in 1999. The vent sites are characterized by white siliceous crusts on top of the sediment layer and by temperatures of up to 48.6°C. Pore waters are enriched in silica and sulfide and show low pH values. The very shallow depth of these vent sites (1050 m) and the influence of volcanic activity particularly control the concentration of pore fluid constituents. Chloride is depleted up to 20 % and the calculated hydrothermal endmember concentration is in the range of 1 to 84 mM. This fluid composition is attributed to phase separation, since other mechanisms for Cl depletion can clearly be ruled out. The depth of phase separation, inferred by using a relationship between Cl concentrations of the phase separated fluids and p,T conditions, is about 1450 m beneath the seafloor at Hook Ridge. Thus, phase separation takes place at subcritical conditions. Whereas the sediments on Hook Ridge are characterized by diffuse outflow of hydrothermal fluids, the hydrothermal impact on the sediments of the NE part of the adjacent King George Basin is shown in deeper sections of these cores (6 m). Depth profiles of elements that are not affected by diagenesis reveal diffusion controlled transport from a reaction layer below the sampling depth. The direct vicinity to the hydrothermally active volcanic edifice Hook Ridge suggests that this reaction layer is within the basal sediments that are heated by the hot crust underneath. This interpretation is confirmed by various geochemical characteristics of the pore fluids from which the temperature of the ... |
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