Open AccessMethane, manganese, and helium‐3 in newly discovered hydrothermal plumes over the Central Indian Ridge, 18°–20°S
Author(s) -
Kawagucci Shinsuke,
Okamura Kei,
Kiyota Kaoru,
Tsunogai Urumu,
Sano Yuji,
Tamaki Kensaku,
Gamo Toshitaka
Publication year - 2008
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2008gc002082
Subject(s) - hydrothermal circulation , geology , methane , basalt , lava , ridge , plume , geochemistry , manganese , mineralogy , seawater , volcano , paleontology , oceanography , chemistry , physics , organic chemistry , thermodynamics
We have investigated newly discovered submarine hydrothermal plumes over the Central Indian Ridge, 18°–20°S. Onshore chemical analyses of methane, its carbon isotope, manganese, and helium‐3 in seawater samples obtained from the plumes revealed their detailed geochemical characteristics. One of the newly discovered hydrothermal plumes located over the western wall of the axial valley at Segment 15B (19°33′S), called the Roger Plateau, showed constant CH 4 /Mn and CH 4 / 3 He ratios throughout the plume. The CH 4 / 3 He ratio (4 × 10 6 ) and δ 13 C (−17.5‰) are consistent with those of basalt‐hosted sediment‐free hydrothermal systems, although the CH 4 /Mn ratio (∼1) is moderately higher. These features are thought to indicate a metal‐depleted fluid chemistry. The other hydrothermal field is located within the axial valley at the northern part of the smooth lava plain at Segment 16 (18°20′S), called the Dodo Great Lava Plain, where several plumes were detected. The CH 4 /Mn and CH 4 / 3 He ratios showed large variation through the plumes while δ 13 C values were almost constant. Geochemical characteristics of venting fluid estimated from those of the plumes were apparently high CH 4 /Mn (>6) and CH 4 / 3 He (>60 × 10 6 ) ratios and low δ 13 C values (<−27.5‰), suggesting possible influences of several methane input processes to the fluid chemistry.