Helium and carbon gas geochemistry of pore fluids from the sediment-rich hydrothermal system in Escanaba Trough |
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| Institution: | 1. I.S. Gramberg All-Russian Research Institute of Geology and Mineral Resources of the World Ocean, Angliiskii pr. 1, Saint Petersburg, 191120, Russia;2. A.P. Karpinsky All-Russian Research Geological Institute, Srednii pr. 74, Saint Petersburg, 199106, Russia;1. Program in Ecology, Evolution, and Conservation Biology, University of Illinois, Urbana, IL 61801, USA;2. University of Maryland Center for Environmental Science, Appalachian Laboratory, Frostburg, MD 21532, USA;3. Department of Stratigraphy and Paleontology, University of Granada, Granada, Spain;4. Department of Plant Biology, University of Illinois, Urbana, IL 61801, USA;5. Department of Geology, University of Illinois, Urbana, IL 61801, USA;1. Research Center for Astronomy and Geosciences, Geobiomineralization and Astrobiological Research Group, Institute for Geology and Geochemistry, Hungarian Academy of Sciences, Budaörsi út. 45, 1112 Budapest, Hungary;2. Eszterházy Károly College, Dept. of Natural Geography and Geoinformatics, Leányka str. 6, 3300 Eger, Hungary;3. Szeged University, Dept. of Mineralogy, Geochemistry and Petrology, Egyetem str. 2-6, 6702 Szeged, Hungary;4. Institute for Nuclear Research, Hungarian Academy of Sciences, Bem tér 18/c, H-4026 Debrecen, Hungary;5. Mangán Ltd, Külterület 1, Úrkút 8409, Hungary;6. Department of Geological Sciences, University of Colorado, 2200 Colorado Avenue, UCB 399, Boulder, CO 80309-0399, USA |
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| Abstract: | Ocean Drilling Program (ODP) Leg 169, which was conducted in 1996 provided an opportunity to study the gas geochemistry in the deeper part of the sediment-rich hydrothermal system in Escanaba Trough. Gas void samples obtained from the core liner were analyzed and their results were compared with analytical data of vent fluid samples collected by a submersible dive program in 1988. The gas geochemistry of the pore fluids consisted mostly of a hydrothermal component and was basically the same as that of the vent fluids. The He isotope ratios (R/RA=5.6–6.6) indicated a significant mantle He contribution and the C isotopic compositions of the hydrocarbons δ13C(CH4)=?43‰, δ13C(C2H6)=?20‰] were characterized as a thermogenic origin caused by hydrothermal activity. On the other hand, the pore fluids in sedimentary layers away from the hydrothermal fields showed profiles which reflected lateral migration of the hydrothermal hydrocarbons and abundant biogenic CH4. Helium and C isotope systematics were shown to represent a hydrothermal component and useful as indicators for their distribution beneath the seafloor. Similarities in He and hydrocarbon signatures to that of the Escanaba Trough hydrothermal system were found in some terrestrial natural gases, which suggested that seafloor hydrothermal activity in sediment-rich environments would be one of the possible petroleum hydrocarbon generation scenarios in unconventional geological settings. |
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