Inactive Hydrothermal Vent Field Discovered at the Southwest Indian Ridge 50.5ºE

The 5th leg of the 2008 Chinese DY115-20 expedition on board R/V Dayangyihao has successfully discovered an inactive hydrothermal vent field at 50.4671°E, 37.6579°S on the ultraslow-spreading Southwest Indian Ridge (SWIR). This inactive hydrothermal field is located on the shallowest portion of Segment 27 of the SWIR west of the Gallieni Transform Fault, with relative low mantle Bouguer gravity anomaly (Sauter, et al., 2001). This newly found site is located in the middle of a ridge segment, where the rift valley disappears and the seafloor depth is 1739 m. This site is about 49 miles east of the first active hydrothermal vent field on Segment 28 (Tao et al., 2007).

Two areas of sulfide deposits within this inactive vent field were confirmed tentatively by video system and nine TV-grabber samples. The size of the first area is about 209 m x 100 m. The second area is about 300 m x 180 m based on interpretation of the videos. Numerous sights of sulfide-rich ores were seen in the video. The collected samples included sulfide, opal chimney, metalliferous sediment, basalt and some hydrothermal fauna. One TV-grabber station contained black sulfide chimneys, chimney fragments, massive sulfide, thin stratiform (0.5-3cm) and small particle sulfide. These samples are dominated by chalcopyrite, pyrite, sphalerite, and even native copper. Preliminary shipboard analyses of massive sulfide and metalliferous sediment samples revealed Cu compositions of up to 8-9% and 5%, respectively. Many dead bivalve shells and some gastropod shells were found in the red metalliferous sediment, indicating that the hydrothermal activity became extinct not long ago.

- Sauter, D., P. Patriat, C. Rommevaux-Jestin, M. Cannat, A. Briais, and Gallieni Scientific Party, The Southwest Indian Ridge between 49°15E and 57°E: Focused accretion and magma redistribution. Earth Planet. Sci. Lett. 192, 303-317, 2001.
- Tao, C., J. Lin, S. Guo, Y.J. Chen, G. Wu, X. Han, C.R. German, D.R. Yoerger, J. Zhu, N. Zhou, X. Sun, E.T. Baker, and DY115-19 Science Party, First discovery and investigation of a high-temperature hydrothermal vent field on the ultraslow spreading Southwest Indian Ridge, AGU Fall Meeting, Abstract #T52B-07, 2007.

Chunhui Tao1*, Guanghai Wu1, Xin Su2, I.V. Egorov3, I.G. Dobretsova4, Hongqiao Zhao1, John Chen10, Ning Zhou5, Junyi Yang1, Zhigang Chen11, Xiguang Deng6, Wei Huang1, Peifeng Zhou1, Tao Ding1, Kai Zhang1, Zhongyan Qiu1, Feng Li7, Xuewen Wu1, Yunda Li8, Yunlu Cui9, Science Party12, Edward T. Baker13

1Key Laboratory of Submarine Geosciences, Second Institute of Oceanography, State Oceanic Administration, 36 Baochubei Road, Hangzhou, Zhejiang, 310012, China; 86-571-88829003,
2China University of Geosciences, School of Ocean Sciences, Beijing, 100083, China
3VNIIOkeangeologia, Saint-Petersburg, 1 Angliysky prospect, 190121, Russia
4Polar Marine Geosurvey Expedition, Saint-Petersburg, Russia
5China Ocean Mineral Resources R&D Association, 1 Fuxingmenwai Ave., Beijing 100860, China
6Guangzhou Marine Geological Survey, Guangzhou, 510640,China
7Pioneer High Technology Corp. , Beijing 100860, China
8Institute of Mineral Resource, China Academe Geology Science, Beijing, 100037, China
9Ocean Survey Instruments & Technology Management Center of NBSOA,22 Fushun Rd. Qingdao, 266033,China,
10Institute of Theoretical and Applied Geophysics, Peking University, Beijing 100871, China
11Xiamen University, Xiamen, 361005, China
12DY115-20 Leg 5 Scientific Party
13Pacific Marine Environmental Laboratory, NOAA, Seattle, WA 98115, USA