Abstract
This paper describes GLORIA sidescan sonar data from a single swath along the Cocos-Nazca Spreading Centre between the 95.5° W propagating rift and the Pacific-Cocos-Nazca triple junction. Almost the whole of the plate boundary was imaged. Five medium sized offsets of the spreading centre, ranging from 10 to 25 km, were seen. Of these, at least one (at 99° W) is a previously unknown propagating rift, propagating westwards away from the Galapagos hotspot at about 40 mm a-1. Two other offsets have some, but not all, of the characteristics of propagating rifts, and may be poorly developed (possibly ‘duelling’) propagating rifts or migrating overlapping spreading centres. In each case the apparent propagation rate is between one and two times the half spreading rate. The average length of ridge segments in this region is 70 km, but lengths range from 12 to 135 km. The longest segments are those immediately behind actively propagating ridge offsets. The overall plan shape of the ridge axis is roughly sinusoidal, with a wavelength of 400–500 km and an amplitude of ±20 km. This nonlinear shape has arisen since the spreading centre was created, and may reflect an instability in the mantle plumes that control ridge segmentation.
Similar content being viewed by others
References
Batiza, R. and Margolis, S. H., 1986, A Model for the Origin of Small Non-Overlapping Offsets (SNOOs) of the East pacific Rise, Nature 320, 439–441.
Christie, D. M. and Sinton, J. M., 1981, Evolution of Abyssal Lavas along Propagating Segments of the Galapagos Spreading Center, Earth Planet Sci. Lett. 56, 321–335.
Hey, R., 1977a, A New Class of ‘Pseudofaults’ and their Bearing on Plate Tectonics: a Propagating Rift Model, Earth Planet. Sci. Lett. 37, 321–325.
Hey, R. N., 1977b, Tectonic Evolution of the Cocos-Nazca Spreading Center, Geol. Soc. Amer. Bull. 88, 1404–1420.
Hey, R. and Vogt, P., 1977, Spreading Center Jumps and Sub-Axial Asthenosphere Flow near the Galapagos Hotspot, Tectonophysics 37, 41–52.
Hey, R., Johnson, G. L., and Lowrie, A., 1977, Recent Plate Motions in the Galapagos Area, Geol. Soc. Amer. Bull. 88, 1385–1403.
Hey, R., Duennebier, F., and Morgan, W. J., 1980, Propagating Rifts on Mid-Ocean Ridges, J. Geophys. Res. 85, 3647–3658.
Hey, R. N., Kleinrock, M. C., Miller, S. P., Atwater, T. M., and Searle, R. C., 1986, Seabeam/Deep-Tow Investigation of an Active Oceanic Propagating Rift System, Galapagos 95.5° W, J. Geophys. Res. 91, 3369–3393.
Hey, R. N., Sinton, J. M., and Duennebier, F. K., 1988, Propagating Rifts and Spreading Centers, In: Decade of North American Geology, vol. N, The Eastern Pacific and Hawaii, Geological Society of America, Boulder, Co. (in press).
Johnson, G. L., Vogt, P. R., Hey, R., Campsie, J., and Lowrie, A., 1976, Morphology and Structure of the Galapagos Rise, Marine Geology 21, 81–120.
Johnson, H. P., Karsten, J. L., Delaney, J. R., Davis, E. E., Currie, R. G., and Chase, R. L., 1983, A Detailed Study of the Cobb Offset of the Juan de Fuca Ridge: Evolution of a Propagating Rift, J. Geophys. Res. 88, 2297–2315.
Klitgord, K. D. and Mudie, J. D., 1974, The Galapagos Spreading Centre: A Near-Bottom Geophysical Survey, Geophys. J. R. astr. Soc. 38, 563–586.
Kleinrock, M. C., Searle, R. C., and Hey, R. N., 1988, Tectonics of the Failing Spreading System Associated with the 95.5° W Galapagos Propagator, J. Geophys. Res. (in press).
LaBrecque, J. L., Kent, D. V., and Cande, S. C., 1977, Revised Magnetic Polarity Time Scale for late Cretaceous and Cenozoic Time, Geology 5, 330–335.
Langmuir, C. H., Bender, J. F., and Batiza, R., 1986, Petrologic and Tectonic Segmentation of the East Pacific Rise, 5°30′ N-14°30′ N, Nature 322, 422–429.
Lonsdale, P., 1985, Non Transform Offsets of the Pacific-Cocos Plate Boundary and their Trace on the Rise Flank, Geol. Soc. Amer. Bull. 96, 313–327.
Macdonald, K. C. and Fox, P. J., 1983, Conjugate Spreading Centers and Degenerate Transform Faults on the East Pacific Rise, Nature 302, 55–58.
Macdonald, K. C., Sempere, J. C., and Fox, P. J., 1984, East Pacific Rise from Siqueiros to Orozco Fracture Zones: Along-Strike Continuity of Axial Neovolcanic Zone and Structure and Evolution of Overlapping Spreading Centres, J. Geophys. Res. 89, 6049–6069.
Macdonald, K. C., Sempere, J. C., and Fox, P. J., 1986, Reply: The Debate concerning Overlapping Spreading Centers and Mid-Ocean Ridge Processes, J. Geophys. Res. 91, 10501–10510.
Macdonald, K. C., Haymon, R. M., and Miller, S. P., 1988, Deep-Tow and Sea Beam Studies of Duelling Propagating Ridges on the East Pacific Rise Near 20°40′ S, J. Geophys. Res. 93, 2875–2898.
Masson, D. G., Cacchione, D. A., and Drake, D. E., 1988, Tectonic Evolution of the Gorda Ridge Inferred from Sidescan Images, Marine Geophys. Res. 10, 191–204.
Munschy, M., 1987, Etude Géophysique Détaillée du Point Triple de Rodriguez et de la Zone Axiale des Trois Dorsales Associées (Océan Indien), Thèse de doctorat, Université Louis Pasteur, Strasbourg.
Phipps Morgan, J. and Parmentier, E. M., 1985, Causes and Rate-Limiting Mechanisms of Ridge Propagation: A Fracture Mechanics Model, J. Geophys. Res. 90, 8603–8612.
Schouten, H., Klitgord, K. D., and Whitehead, J. A., 1985, Segmentation of Mid-Ocean Ridges, Nature 317, 225–229.
Searle, R. C., 1984, GLORIA Survey of the East Pacific Rise near 3.5° S: Tectonic and Volcanic Characteristics of a Fast-Spreading Mid-Ocean Rise, Tectonophys. 101, 319–344.
Searle, R. C. 1986, GLORIA Investigations of Oceanic Fracture Zones: Comparative Study of the Transform Fault Zone, J. Geol. Soc. London 143, 743–756.
Searle, R. C. and Francheteau, J., 1986, Morphology and Tectonics of the Galapagos Triple Junction, Marine Geophys. Res. 8, 95–129.
Searle, R. C. and Hey, R. N., 1983, GLORIA Observations of the Propagating Rift at 95.5° W on the Cocos-Nazca Spreading Center, J. Geophys. Res. 88, 6433–6447.
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.
Tamsett, D. and Searle, R. C., 1988, Structure and Development of the Midocean Ridge Plate Boundary in the Gulf of Aden: Evidence from GLORIA Sidescan Sonar, J. Geophys. Res. 93, 3157–3178.
Vogt, P. R. and deBoer, J., 1976, Morphology, Magnetic Anomalies and Basalt Magnetization at the Ends of the Galapagos High-Amplitude Zone, Earth Planet. Sci. Lett. 33, 145–163.
Whitehead, J. A., Dick, H. J. B., and Schouten, H., 1984, A Mechanism for Magmatic Accretation under Spreading Centres, Nature 312, 146–147.
Wilson, D. S., Hey, R. N., and Nishimura, C., 1984, Propagation as a Mechanism of Reorientation of the Juan de Fuca Ridge, J. Geophys. Res. 89, 9215–9225.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Searle, R.C. Location and segmentation of the Cocos-Nazca spreading centre west of 95° W. Marine Geophysical Researches 11, 15–26 (1989). https://doi.org/10.1007/BF00286245
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00286245