Abstract
High alkalinity ( > 1.8 mmol kg-1), pH (4.7-5.3), and ammonium ( ∼ 5 mmol kg-1) in hydrothermal fluids from the JADE and CLAM sites in the Mid-Okinawa Trough back-arc basin demonstrate organic matter decomposition during high-temperature fluid-sediment interaction. The endmember fluid from the JADE site ( ∼ 320°C black smoker), which is free of Mg and SO4, has similar chemical characteristics as those at the Escanaba Trough, one of the representative sediment-hosted ridge systems in the eastern Pacific. On the other hand, fluid samples from the CLAM site ( ∼ 100°C) show remarkably high alkalinity (10.3 mmol kg-1) comparable to the highest alkalinity of 10.6 mmol kg-1 (Guaymas Basin) yet observed in hydrothermal fluids, and significantly higher δ34S of SO4 ( > 25‰) than ambient seawater (21‰). It is suggested that sulfate reduction plays a dominant role in decomposing organic matter to increase alkalinity in the CLAM site. Variation of the δ34S values of H2S (from -0.2 to +3.0‰) in the CLAM fluids taken from different vents suggests that the CLAM site should consist of multiple local hydrothermal systems in different evolutionary stages with regard to sulfate reduction.
Original language | English |
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Pages (from-to) | 328-338 |
Number of pages | 11 |
Journal | Earth and Planetary Science Letters |
Volume | 107 |
Issue number | 2 |
DOIs | |
Publication status | Published - Nov 1991 |
Externally published | Yes |
All Science Journal Classification (ASJC) codes
- Geophysics
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science