Marine Geophysical Researches

, Volume 19, Issue 6, pp 535–552 | Cite as

Evolution of the Axial Geometry of the Southwest Indian Ocean Ridge between the Melville Fracture Zone and the Indian Ocean Triple Junction – Implications for Segmentation on Very Slow-Spreading Ridges

  • Lindsay Parson
  • Daniel Sauter
  • Véronique Mendel
  • Philippe Patriat
  • Roger Searle


Geophysical data from 900 km of the Southwest Indian Ridge are used todescribe the pattern of evolution of the plate boundary between 61° Eand 70° E over the past 20 million years. The SWIR is anobliquely-opening, ultra slow-spreading axis, and east of61° E comprises a series of ridge sections, each about 100–120 kmin length. The orientation of these sections varies fromsub-orthogonal to oblique to the approximately N–S spreadingdirection. In general, the suborthogonal sections are shallower, commonlysubdivided into an array of discrete axial segments, and carry recognisablecentral magnetic anomalies. The majority of the oblique sections are single,continuous rifts without continuous axial magnetic signatures.Morphotectonics of the Southwest Indian Ridge crust have not previously beenwell constrained off-axis, and we here present sidescan sonar andswath bathymetric data up to 100 km from the ridge to demonstrate the complexities of its spatial and temporal evolution.A model is proposed that the segmentation style correlates with analong-axis variation between: (a) relatively thick crustal sections which overlie mantle sections with higher magmatic supply created in orthogonally-spreading segments and (b) those oblique sections associated with cooler, magmatically-starved mantle and thinner crust. These latter sections are formed at broad offset zones in theplate boundary, more precisely defined on faster-spreading ridges asnontransform discontinuities. The nonsystematic pattern of crustalconstruction, extensional basin formation and the absence of extension-parallel traces of discontinuities off-axis suggest that the oblique spreading sections are not fixed in space or time.


Indian Ocean Magnetic Anomaly Oblique Section Extensional Basin Southwest Indian Ocean 
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  1. Blondel, Ph. and Murton, B. J., 1997, Hand Book of Seafloor Sonar Imagery. Wiley and Sons, 314 pp.Google Scholar
  2. Cannat, M., 1996, How Thick is the Magmatic Crust at Slow-Spreading Mid-Ocean Ridges?, J. Geophys. Res. 101(B2), 2847–2857.Google Scholar
  3. Cannat, M. et al., 1995, Thin Crust, Ultramafic Exposures and Rugged Fault Patterns at the Mid-Atlantic Ridge (22°-24°). Geology 23, 49–52.Google Scholar
  4. Edgar, N. T., Dillon, W. P., Jacoñs, C. L., Parson, L. M., Scanlon, K. M., and Holcomñe, T. L., 1990, The Structure and Spreading History of the Cayman Trough, Trans. 12th Cariññean Geol. Conf. St Croix, July 1989, 11 pp.Google Scholar
  5. Dauteuil, O and Brun, J.-P., 1996, Deformation Partitioning in a Slow Spreading Ridge Undergoing Oñlique Extension: Mohns Ridge, Norwegian Sea, Tectonics 15(4), 870–884.Google Scholar
  6. German, C. R., Parson, L. M., and HEAT Scientific Team, 1996, Hydrothermal Exploration Near the Azores Triple Junction: Tectonic Control of Venting at Slow-Spreading Ridges? Earth Planet. Sci. Lett. 138, 93–104.Google Scholar
  7. Grindlay, N. R., and Fox, P. J., 1994, Lithospheric Stresses Associated with Nontransform Offsets of the Mid-Atlantic Ridge-Implications from a Finite Element Analysis, Tectonics 13, 733.Google Scholar
  8. Grindlay, N. R., Fox, P. J., and Macdonald, K. C., 1991, Second-Order Ridge Axis Discontinuities in the South Atlantic: Morphology, Structure, and Evolution, Mar. Geophys. Res. 13, 21–49.Google Scholar
  9. Hey, R. N., Johnson, P. D., Martinez, F., Korenaga, J., Somers, M. L., Huggett, Q. J., LeBas, T. P., Rusñy, R. I., and Naar, D. F., 1995, Plate Boundary Reorganisation at a Large-Offset, Rapidly Propagating Rift, Nature 378, 167–170.Google Scholar
  10. Jacoñs, C. L., Edgar, N. T., Parson, L. M., Dillon, W. P., Scanlon, K. M., and Holcomñe, T. L., 1989, A Revised Bathymetry of the Mid-Cayman Rise and Central Cayman Trough using Long Range Side-Scan Sonar. Institute of Oceanographic Sciences Deacon Lañoratory, Report No. 272, 11 pp. & chart.Google Scholar
  11. Karson, J. A., 1990, Seafloor Spreading on the Mid-Atlantic Ridge: Implications for the Structure of Ophiolites and Oceanic Lithosphere Produced in Slow-Spreading Environments, in Malpas, J., Moores, E. M., Panayyiotou, A., and Xenophontos, C. (eds.), Proc. Symposium on Ophiolites and Oceanic Lithosphere-TROODOS 87, Geological Survey Department, Ministry of Agriculture and Natural Resources, Nicosia, Cyprus.Google Scholar
  12. Laughton, A. S., 1980, The First Decade of GLORIA, J. Geophys. Res. 86(B12), 11511–11534.Google Scholar
  13. Lin, J. and Phipps Morgan, J., 1992, The Spreading Rate Dependance of Three Dimensional Mid-Ocean Ridge Gravity Structure, Geophys. Res. Lett. 19, 13–16.Google Scholar
  14. Lin, J., Purdy, G. M., Schouten, H., Sempere, J-C., and Zervas, C., 1990, Evidence from Gravity Data for Focussed Magmatic Accretion along the Mid-Atlantic Ridge, Nature 344, 627–632.Google Scholar
  15. Macdonald, K. C., Fox, P. J., Perram, L. J., Eisen, M. F., Haymon, R. M., Miller, S. P., Carñotte, S. M., Cormier, M-H. and Shor, A. N., 1988, A New View of the Mid-Ocean Ridge from the Behaviour of Ridge Axis Discontinuities, Nature 335, 217–225.Google Scholar
  16. Mendel, V., Sauter, D., Parson, L. M., and Vanney, J-M., 1997, Segmentation and Morphotectonic Variations along a Super Slow-Spreading Center: The Southwest Indian Ridge, Mar. Geophys. Res. 19, 503–531 (this issue).Google Scholar
  17. Mevel, C. et al., 1998, Rapport de Mission, Marion Dufresne Cruise MD107. 8 August-10 Septemñer, 1997, 183 pp.Google Scholar
  18. Mitchell, N. C., 1989, Investigation of the Structure and Evolution of the Indian Ocean Triple Junction using GLORIA and other Geophysical Techniques. PhD thesis, unpuñlished, Oxford University.Google Scholar
  19. Mitchell, N. C., 1991, Distriñuted Extension at the Indian Ocean Triple Junction, J. Geophys. Res. 96, 8019–8043.Google Scholar
  20. Mitchell, N. C. and Parson, L. M., 1993, The Tectonic Evolution of the Indian Ocean Triple Junction, Anomaly 6 to Present, J. Geophys. Res. 98, 1793–1812.Google Scholar
  21. Munschy, M. and Schlich, R., 1989, The Rodrigues Triple Junction (Indian Ocean): Structure and Evolution for the Past One Million Years, Mar. Geophys. Res. 11,1–14.Google Scholar
  22. Murton, B. J. and Parson, L. M., 1993, Segmentation, Volcanism and Deformation of Oñlique Spreading Centres: A Quantitative Study of the Reykjanes Ridge, Tectonophysics 222(2), 237–257.Google Scholar
  23. Parson, L. M., et al., 1987, RRS ‘Charles Darwin’ Cruise 23/87, 13 May-11 June, 1987. Geophysical Investigation of the Indian Ocean Triple Junction, Institute of Oceanographic Sciences Deacon Lañoratory Cruise Report No. 201, 24 pp.Google Scholar
  24. Parson, L. M., Murton, B. J., Searle, R. C., Booth, D., Evans, J., Field, P., Keeton, J., Laughton, A., McAllister, E., Millard, N., Redñourne, L., Rouse, I., Shor, A., Smith, D., Spencer, S., Summerhayes, C., and Walker, C., 1993, En Echelon Axial Volcanic Ridges at the Reykjanes Ridge: A Life Cycle of Volcanism and Tectonics, Earth Planet. Sci. Lett. 117(1/2), 73–87.Google Scholar
  25. Patriat, Ph., 1987, Reconstitution du systeme de dorsales de l'Ocean Indien par les methodes de la cinematique des plaques. Edition des TAFF, p. 308. Unpuñlished PhD thesis.Google Scholar
  26. Patriat, Ph. and Parson, L. M., 1989, A Survey of the Indian Ocean Triple Junction within the Antarctic Plate. Implications for the Junction Evolution Since 15 Ma, Mar. Geophys. Res. 11, 89–100.Google Scholar
  27. Patriat, Ph., Sauter, D., Munschy, M., and Parson, L. M., 1997, A Survey of the SWIR Axis Between the Atlantis II FZ and the Indian Ocean Triple Junction: Regional Setting and Large Scale Segmentation, Mar. Geophys. Res. 19, 457–480 (this issue).Google Scholar
  28. Phipps Morgan, J. and Parmentier, E. M., 1984, Lithospheric Stress Near a Ridge-Transform Intersection, Geophys. Res. Lett. 11, 113–116.Google Scholar
  29. Roñinson, P. T., Von Herzen, R., et al., 1989, Proc. ODP, Init. Repts., 118: Copllege Station. Tx (Ocean Drilling Program).Google Scholar
  30. Sauter, D. and Mendel, V., 1997, Variations of Backscatter Strength along the Super Slow-Spreading Southwest Indian Ridge ñetween 57° and 70° E, Mar. Geol., in Press.Google Scholar
  31. Searle, R. C. and Laughton, A. S., 1977, Sonar Studies of the Mid-Atlantic Ridge and Kurchatov Fracture Zone, J. Geophys. Res. 82, 5313–5328.Google Scholar
  32. Searle, R. C. and Laughton, A. S., 1981, Fine Scale Sonar Study of Tectonics and Volcanism on the Reykjanes Ridge, Oceanologica Acta, No. SP. Proc. 26th Int. Geol. Congr., Paris. 5–13.Google Scholar
  33. Searle, R. C., Keeton, J. A., Owens, R., Mecklenñurgh, R., White, R. S., Parsons, B., and Lee, S. M., 1997, The Reykjanes Ridge: Structure and Tectonics of a Hot-Spot Influenced, Slow-Spreading Ridge, from Multiñeam Bathymetric, Gravity and Magnetic Investigations, Earth Planet. Sci. Lett., under revision.Google Scholar
  34. Sempere, J.-C., Lin, J., Brown, H. S., Schouten, H., and Purdy, G. M., 1993, Segmentation and Morphotectonic Variations along a Slow Spreading Center: The Mid-Atlantic Ridge (24°00′ N-30°40′ N), Mar. Geophys. Res. 15(3), 153–200.Google Scholar
  35. Somers, M. L., Carson, R. M., Revie, J. A., Edge, R. H., Barrow, B. J., and Andrews, A. G., 1978, GLORIA-II-An Improved Long-Range Sidescan Sonar, in Oceanology International, BPS Exhiñitions Ltd., London, pp. 16–24.Google Scholar
  36. Tapscott, C. R., Patriat, P., Fisher, R. L., Sclater, J. G., Hoskins, H., and Parsons, B., 1980, The Indian Ocean Triple Junction, J. Geophys. Res. 85(B9), 4723–4739.Google Scholar
  37. Taylor, R. N., Thirlwall, M. F., and Murton, B. J., 1995, Spatial Geochemical Variation along the Reykjanes Ridge, Terra Nova 7, 145.Google Scholar
  38. Tucholke, B. E., 1992, Massive Suñmarine Rockslide in the Rift-Valley Wall of the Mid-Atlantic Ridge, Geology 20(2), 129–132.Google Scholar
  39. Tucholke, B. E. and Lin, J., 1994, A Geological Model for the Structure of Ridge Segments in Slow Spreading Ocean Crust, J. Geophys. Res. 99, 11,937–11,958.Google Scholar
  40. White, R. S., 1997, Rift-Plume Interaction in the North Atlantic, Philosoph. Trans. Roy. Soc., London, 355, 319–339.Google Scholar

Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • Lindsay Parson
    • 1
  • Daniel Sauter
    • 2
  • Véronique Mendel
    • 2
  • Philippe Patriat
    • 3
  • Roger Searle
    • 4
  1. 1.Southampton Oceanography CentreSouthamptonU.K
  2. 2.Ecole et Observatoire des Sciences de la TerreInstitute de Physique du GlobeStrasbourgFrance
  3. 3.Institute de Physique du GlobeParisFrance
  4. 4.Department of Earth Sciences, Science LaboratoriesDurham UniversityDurhamU.K

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