Diversity of fluid geochemistry affected by processes during fluid upwelling in active hydrothermal fields in the Izena Hole, the middle Okinawa Trough back-arc basin

Jun Ichiro Ishibashi, Takuroh Noguchi, Tomohiro Toki, Shunsuke Miyabe, Shosei Yamagami, Yuji Onishi, Toshiro Yamanaka, Yuka Yokoyama, Eriko Omori, Yoshio Takahashi, Kenta Hatada, Yuzuru Nakaguchi, Motoko Yoshizaki, Uta Konno, Takazo Shibuya, Ken Takai, Fumio Inagaki, Shinsuke Kawagucci

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)

Abstract

Two active hydrothermal fields, Jade and Hakurei fields have been discovered within the Izena Hole, a rectangular 6 km × 3 km shape depression located in the middle Okinawa Trough back arc basin. In both fields, intense hydrothermal activity is represented by venting of high-temperature fluid (>300°C) and occurrence of sulfide/sulfate ore deposits. We collected hydrothermal fluids during dive expeditions of ROV Hyper Dolphin conducted in 2003, 2010 and 2011, in order to analyze both elemental and gas species. The geochemistry of high temperature hydrothermal fluids collected from the Jade and Hakurei fields is very similar to each other with exceptions in minor gas composition. Little temporal variation was observed in geochemistry of the high-temperature hydrothermal fluid of the Jade field over two decades, since a previous study carried out in 1989. These results suggest that these fluids are derived from a common fluid reservoir where fluid chemistry is basically controlled by fluid-mineral equilibria and gas species are dominantly contributed from the same magma. Venting of low temperature fluid (about 104°C) was discovered in the distal part of the Jade field, which was named as the Biwako vent. Chemical composition of the Biwako vent fluid was distinctive from that of the high temperature fluid in the proximal part of the Jade field, and could not be explained by simple dilution or cooling. This intra-field chemical diversity could be caused by phase separation and segregation during fluid upwelling, based on relationships in concentrations of Cl and major cations. On the other hand, the chemical diversity recognized in minor gas composition between the Jade and Hakurei fields is in accordance with results from previous plume survey. Difference in concentrations of minor gases such as H2 is attributed to contribution from thermal degradation of organic matter in the sediment, during fluid upwelling.

Original languageEnglish
Pages (from-to)357-369
Number of pages13
JournalGEOCHEMICAL JOURNAL
Volume48
Issue number4
DOIs
Publication statusPublished - Jan 1 2014

Keywords

  • Fluid-sediment interactions
  • Hydrothermal fluid circulation system
  • Magmatic volatiles
  • Okinawa Through
  • Phase separation
  • Thermal decomposition of organic matter

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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