Helium and carbon geochemistry of hydrothermal fluids from the North Fiji Basin spreading ridge (southwest Pacific)

Jun Ichiro Ishibashi, Hiroshi Wakita, Yukihiro Nojiri, Daniel Grimaud, Philippe Jean-Baptiste, Toshitaka Gamo, Jean Marie Auzende, Tetsuro Urabe

研究成果: ジャーナルへの寄稿学術誌査読

54 被引用数 (Scopus)

抄録

The North Fiji Basin is one of the active marginal basins in the southwestern Pacific. Hydrothermal fluid emanations were located at two sites on the Central ridge of the basin. High-temperature fluids (230-290°C) venting from anhydrite chimneys at a 17°S site have end-member compositions of: 11.0-14.5 mmol/kg of CO2; 30.4-43.5 μmol/kg of CH4; and 2.3-4.5 × 10-5 cm3STP/g of He. Taking phase separation processes into account, the gas abundances are not enriched compared with the mid-oceanic ridge hydrothermal systems. Isotopic compositions of CO213C = -6.2 to -5.7‰PDB), CH413C = -20 to -18‰PDB), and helium ( R RA = 9.0-10.0) are comparable to the mid-oceanic ridge signature. Together with basalt helium data, the helium isotopic signature may be attributed to the incorporation of a hotspot-like primitive component. Low-temperature shimmering fluids (the highest measured temperature was 5.2°C) associated with biological communities at a site at 18°50′S show slight chemical anomalies, in some species, in SiO2, Mn, Li, pH and CH4, and helium isotope ratios distinct from ambient seawater. Evaluated helium isotopic compositions prior to dilution fall between R RA = 8.4 and 8.9, supporting the suggestion of high-temperature hydrothermal activity at this site, although this was not observed by dive expeditions. The gas geochemistry of these two different types of fluids show several similar characteristics to the mid-oceanic ridge hydrothermal systems. This result is in accordance with previous petrological studies which demonstrated a dominant N-MORB source signature and a co-existing OIB source influence of the North Fiji Basin magmatism.

本文言語英語
ページ(範囲)183-197
ページ数15
ジャーナルEarth and Planetary Science Letters
128
3-4
DOI
出版ステータス出版済み - 12月 1994
外部発表はい

!!!All Science Journal Classification (ASJC) codes

  • 地球物理学
  • 地球化学および岩石学
  • 地球惑星科学(その他)
  • 宇宙惑星科学

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