Marine barite in sediments from deep sea drilling project sites 424 and 424a (Galapagos hydrothermal mounds field) |
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| Institution: | 1. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan;2. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan;3. Research Center for the Evolving Earth and Planets, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan;4. Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan;5. Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan |
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| Abstract: | The distribution of barite in sediments from D.S.D.P. sites 424 and 424A at the Galapagos hydrothermal mounds field is determined and the process of its formation is deduced. Barite in these deposits is associated with calcareous sediments and is completely absent from the hydrothermal material (manganese crusts and nontronite). Its concentrations tend to increase in the deeper sediments. Since manganese crusts contain significant amounts of Ba, a lack of barite in them is probably due to low concentrations of SO42 in the sediment-seawater interface where they form. The formation of barite occurs within buried sediments, the interstitial waters of which are saturated with SO42. The most probable source of SO42? is the oxidation of H2S which is released from the hydrothermal fluids percolating upwards through the sediments. Although nontronite is formed within buried sediments the environmental conditions occurring during its formation (reducing) prevent barite formation.The association of barite with calcareous sediments is due to the release of Ba by calcareous microorganisms and/or to high concentrations of Ca in the pore waters which maintain a high pH and hence SO42? is stable. |
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