Southwest Indian Ridge Working Group

Chair: Catherine Mével

Working Group Members:
Spain - Miquel Canals
India - Rajendra Kumar Drolia
UK - Chris German
USA - Nancy Grindlay
Japan - Toshihiko Kanazawa
USA - Charlie Langmuir
South Africa - Anton Le Roex
UK - Chris MacLeod
Germany - Jonathan Snow
USA - Cindy Lee Van Dover

This working groups objective was to coordinate reconnaissance mapping and sampling of the Southwest Indian Ridge. Formed in 1997, this working group fused in 2001 with the other successful working group "Arctic Ridges" to make up the Ultraslow Spreading Ridges Working Group in 2004

2001 - SWIR Working Group Update

Reprinted from InterRidge News 10.2 (November 2001)
by Catherine Mével, Chair

Ten years ago there was very little knowledge about this ultra slow ridge. Now we have complete bathymetric coverage of the ridge from the RTJ to the BTJ. This is a major achievement which has been facilitated by the InterRidge programme. In parallel to the mapping, a systematic sampling of the ridge axis has been conducted. It is now possible to evaluate the influence of the Marion and Bouvet hotspots on the ridge, both on the morphology and the chemistry. however, seismic studies are still required to understand the deep structure of the ridge.

Hydrothermal activity along this ridge is still very poorly known. Several nephelometry signals have been documented with MAPRs mounted on the TOBI cable between 58° and 65°E. Moreover, dead chimneys have been collected at 64°E. Hydrothermal deposits associated with serpentinites have also been documented in the eastern portion of the ridge. To date, however, no active field with associated biology has been observed. Further studies are required to get some idea about the distribution of hydrothermal activity on this ultra slow spreading ridge.

A workshop to synthesise the current knowledge gained and to decide future research on the Indian Ridge has been scheduled. The SWIR working group will be terminated at the workshop to be held in April 17 - 19, SOC, UK.

2000 - SWIR Working Group Update

Reprinted from InterRidge News 9.2 (November 2000)
by Catherine Mével, Chair

Miquel Canals (Spain)
Chris German (UK)
Nancy Grindlay (USA)
Charlie Langmuir (USA)
Anton le Roex (South Africa)
Chris MacLeod (UK)
Jonathan Snow (Germany)
Kensaku Tamaki (Japan)
Cindy Lee Van Dover (USA)

The SWIR project plan was initiated in 1997. It is now time to consider what has been accomplished since then and what is still left to do. With two cruises scheduled in early 2001, a complete bathymetric and gravity coverage of the SWIR should be achieved by mid-2001. Furthermore, relatively regular sampling along the ridge axis will have been completed, although at various scales, depending on the area. InterRidge has been influential in the organization of segment scale investigations in the eastern, the particularly cold portion of the ridge (FUJI and INDOYO cruises : Japan, France, UK, Germany : TOBI coverage to investigate magmatic/tectonic interactions, SHINKAI 6500 dives). Some evidence for hydrothermal activity has been documented (nephelometry anomalies, dead chimneys) but no active hydrothermal field sites have been discovered to date.

Detailed geological investigation of one specific area, the Atlantis bank (57°E), around ODP Site 735B, is still under progress (mapping, dregding, ROV, SHINKAI 6500) dives. It is an international effort involving the US, Japan, Canada and UK, linked with ODP.
Biologists have expressed a strong interest in the SWIR because it forms a link between the western Pacific and the South Atlantic ridge systems, naturally, in the absence of documented active hydrothermal fields the biology is still completely unknown on the SWIR. To locate an active site, the necessary next step is to conduct a water column sampling cruise.

Further investigations at regional and local scales are still necessary:
- off-axis studies (temporal variation) to better understand dissymmetry between the two flanks
- determination of crustal structure and lithosphere thickness in areas of different thermal regimes
- seafloor observations and sampling (ROV, submersible) - including, hopefully, an active hydrothermal site

Additionally, the potential for deployment of hydrophones to monitor the seismicity of the eastern potion of the ridge will be explored through consultation with C. Fox.

Scheduled/approved cruises
- water sampling and observations at the Rodrigues Triple Junction, looking for hydrothermal plumes. R/V Kaire and ROV Kaiko, (Japan) PI: Jun Hashimoto, Aug. 2000
- Geology and sampling of Atlantis II Bank. R/V Kaire + ROV Kaiko – PI : E. Kikawa (Japan) and H. Dick (USA), September 2000,
- mapping and sampling the SWIR from 9 to 22° E. MAPRs. Additional proposal to deploy OBSs, to be recovered one year later is still pending. December 2000 - January 2001 - PI : H. Dick and J. Lin (USA). Cape Town 9th Dec. and returns 29th Jan to Durban
- SWIFT : mapping and sampling of the western portion of SWIR from 49° to 35°E. Marion Dufresne - PI: E. Humler (France + Denmark). Feb - March 2001
- Detailed plume biogeochemical prospecting at the Rodrigues Triple Junction. (and possible extension to the easternmost portion of the SWIR), approved but not yet scheduled. PI: C. German and P. Tyler (UK) likely in 2001

Proposed cruises
- seimic tomography of a segment : the Jourdannes mountain
TOM SWIR. PI: D. Sauter (France)

Well evaluated, not scheduled yet
France + Germany + Japan

SWIR Workshop
By mid-2001 a lot more data will be available and a workshop is proposed to synthesise current knowledge, identify areas, both disciplinary and geographically that require investigation and decide on future direction of research in this area. The workshop in planned in early 2002.

1998 - SWIR Working Group Update

Reprinted from InterRidge News 7.2 (Oct. 1998)
by Catherine Mével, Chair

This working group acts to coordinate cruises and proposals to investigate the ultraslow spreading SWIR. There have been four cruises to the SWIR since the summer of 1997, and more are proposed or scheduled for the future.

Completed Cruises
* EDUL, Marion Dufresne, Aug. 1997, PI: Mével. Sampling of the SWIR, 49°-69°E.
* FUJI, Marion Dufresne, Oct. 1997, PIs: Mével, Tamaki. Colloborative French, Japanese and British cruise which made TOBI surveys, OBS deployments and water sampling near the Melville FZ.
* ODP Leg 176, Joides Resolution, Oct/Nov 1997, Co-chiefs: Dick, Natland. Deepening of Hole 735B to 1500 m depth.
* James Clark Ross, April 1998, PIs: Dick, McLeod, Robinson. Used ROPOS to examine the geology of the lower crust with deep-towed magnetics and testing new hard-rock drill.

Scheduled Cruises
* MODE'98, leg 3, Yokosuka/Shinkai6500, Sept./Oct 1998, PI: Fujimoto. Diving in eastern part of the SWIR to areas selected from the FUJI data - volcanism/tect-onism and hydrothermal objectives
* MODE'98, leg 4, Yokosuka/Shinkai6500, Oct./Nov. 1998, PIs: Matsumoto, Dick. Diving on Atlantis II bank

Proposed but not yet funded
* Bathymetric/geophysical survey and sampling of the central portion of the SWIR. PI: Mahoney
* Bathymetric/geophysical survey and sampling of the western portion of the SWIR to the BTJ. PI: Dick
* Off-axis survey of the eastern portion of the SWIR (to the RTJ trace). PIs: Patriat, Sauter
* The Italians plan to start working along the SWIR starting from the Bouvet Triple Junction

There will be a special session at the Fall AGU meeting: T08: Accretionary processes at ultra-low spreading ridges: recent field results from the Arctic and the South West Indian Ridge. The convenors will be K. Crane, C. Mével, K. Tamaki, B. Coakley and J. Georgen.

There has been some preliminary discussions about organizing a SWIR workshop in 1999 or 2000 to synthesize recent results and to organize future plans.

1997 - SWIR Working Group Update

Reprinted from InterRidge News 6.1 (March 1997)
by Catherine Mével, Chair

Although super-slow-spreading ridges make up a significant portion of the ridge system, we still know very little about them. For this reason the InterRidge program decided sometime ago to concentrate efforts on the South West Indian Ridge as an example of a super slow-spreading ridge to understand accretionary processes in these settings. A SWIR working group, chaired by Charlie Langmuir, was set up by InterRidge to discuss the primary scientific to address in the forthcoming years and generated a Project Plan.

The task of the SWIR Implementation Group , created by InterRidge in the fall of 1996, will be to implement that plan. Its mandate is to promote and coordinate research on the SWIR. Clearly an international effort is needed. The bathymetric and geophysical coverage is uncomplete. We have little constrains on the lithosphere thickness beneath the axis, or on the width of the active zone. Except in a few areas, sampling has been done mostly in fracture zones. A systematic sampling of the axis, at both regional and local scales, is missing. The area has not been surveyed for hydrothermal activity. We expect to fill most of these gaps in knowledge and contribute to a better understanding of the global ridge system. The objective is to collect a critical dataset to compare slow- and fast- spreading ridges, in order to better constrain the influence of spreading rate and mantle temperature on accretionary processes.

Future actions on the SWIR
At this stage, two investigative directions are being pursued:
- meso-scale studies along the SWIR axis and off-axis; these investigations should help select areas for local scale studies, and hopefully locate hydrothermal activity.
- studies around ODP Hole 735B, located on the transverse ridge of the Atlantis II fracture zone, to better constrain the geological setting of this hole and the crustal architecture.

Scheduled cruises:
- EDUL- August 1997, Marion Dufresne. PI: Catherine Mével. Sampling of the SWIR axis between the Rodrigues triple junction and 49ºE (rock cores, dredges) to look at regional and segment scale variations. Hydrocasts are also planned for an exploratory investigation of anomalies in the water column.
- FUJI - Oct. 1997, Marion Dufresne. Co-PIs: Kensaku Tamaki and Catherine Mével. TOBI survey and deployment of OBSs on the SWIR axis between 56 and 66ºE.
- ODP leg 176- 15 Oct. -10 Dec. 1997, Joides Resolution. co-PIs: Henry Dick and Jim Natland. Deepening of ODP Hole 735B, at the Atlantis II fracture zone, into more gabbros and hopefully ultramafics.
- R/V Sonne, 1997 or 1998. PI:Chris MacLeod. Geological fine scale mapping and sampling of the platform around 735B using a newly developed drill core.
- 1998, ship? Pis: Henry Dick and Paul Robinson. Geological fine scale observation and mapping of the platform around 735B, using the Canadian ROPOS.

Proposed cruises:
- FRIMAS - 1998, Marion Dufresne. Co-PIs: Philippe Patriat and Daniel Sauter. Bathymetric and geophysical mapping of the crust generated at the SWIR from the axis to the triple junction trace around 63ºE.

The Japanese also have plans to bring the submersible SHINKAI to the SWIR in 1998-1999.

If you have a funded cruise, plan to submit a proposal, or would like to be involved in research on the SWIR, please contact the SWIR working group.