Marine Geophysical Researches

, Volume 8, Issue 2, pp 95–129

Morphology and tectonics of the Galapagos Triple Junction

  • R. C. Searle
  • J. Francheteau


We describe the results of GLORIA and SEABEAM surveys, supplemented by other marine geophysical data, of the Galapagos Triple Junction where the Pacific, Cocos and Nazca plates meet. The data allowed detailed topographic and tectonic maps of the area to be produced. We located each spreading axis with a precision of about 1 km. All three plate boundaries change character as the triple junction is approached to take on morphologies typical of slower spreading axes: the fast-spreading East Pacific Rise develops the morphology of a medium-spreading rise, and the medium-spreading Cocos-Nazca Rise takes on the appearance of a slow-spreading ridge. The axis of the East Pacific Rise was found to be completely continuous throughout the survey area, where it runs along the 102°05′ W meridian. The Cocos-Nazca axis, however, fails to meet it, leaving a 20-km-wide band of apparently normal East Pacific Rise crust between its tip and the East Pacific Rise axis. As a consequence there must be considerable intra-plate deformation within the Cocos and Nazca plates. A further 40 km of the Cocos-Nazca axis is characterised by oblique faulting that we interpret to be a sign of rifting of pre-existing East Pacific Rise crust. We infer that true sea-floor spreading on the Cocos-Nazca axis does not begin until 60 km east of the East Pacific Rise axis. Other areas of similar oblique faulting occur on the Pacific plate west of the triple junction and along the rough-smooth boundaries of the Galapagos Gore. We present a model involving intermittent rifting, rift propagation, and sea-floor spreading, to explain these observations.


  1. Ballard, R. D., Holcomb, R. T., and Van Andel, T.: 1979, ‘The Galapagos Rift at 86°W: 3 — Sheet Flows, Collapse Pits and Lava Lakes of the Rift Valley’, J. Geophys. Res. 84, 5407–5422.Google Scholar
  2. Ballard, R. D., Van Andel, T. H., and Holcomb, R. T.: 1982, ‘The Galapagos Rift at 86°W: 5 —Variations in Volcanism, Structure and Hydrothermal Activity along a 30-km Segment of the Rift Valley’, J. Geophys. Res. 87, 1149–1161.Google Scholar
  3. Corliss, J. B., Dymond, J., Gordon, L. I., Edmond, J. M., Von Herzen, R. P., Ballard, R. D., Green, K., Williams, D., Bainbridge, A., Crane, K., and Van Andel, T. H.: 1979, ‘Submarine Thermal Springs on the Galapagos Rift’, Science 203, 1073–1083.Google Scholar
  4. CYAMEX: 1981, ‘First Manned Submersible Dives on the East Pacific Rise at 31°N (Project RITA): General Results’, Mar. Geophys. Res. 4, 345–379.Google Scholar
  5. 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.Google Scholar
  6. Hey, R. N.: 1977b, ‘Tectonic Evolution of the Cocos-Nazca Spreading Centre’, Geol. Soc. Amer. Bull. 88, 1404–1420.Google Scholar
  7. Hey, R. N., Deffeyes, K. S., Johnson, G. L., and Lowrie, A.: 1972, ‘The Galapagos Triple Junction and Plate Motions in the East Pacific’, Nature 237, 20–22.Google Scholar
  8. Hey, R., Johnson, G. L., and Lowrie, A.: 1979, ‘Recent Plate Motions in the Galapagos Area’, Geol. Soc. Amer. Bull. 88, 1385–1403.Google Scholar
  9. Hey, R. N., Kleinrock, M. C., Miller, S. P., Atwater, T. M., and Searle, R. C.: 1985, ‘Seabeam/Deeptow Investigation of an Active Oceanic Propagating Rift System’, J. Geophys. Res. (in press).Google Scholar
  10. Holden, J. C. and Dietz, R. S.: 1972, ‘Galapagos Gore, NazCoPac Triple Junction and Carnegie/Cocos Ridges’, Nature 235, 266–269.Google Scholar
  11. Johnson, G. L., Vogt, P. R., Hey, R., Campsie, J., and Lowrie, A.: 1976, ‘Morphology and Structure of the Galapagos Rise’, Mar. Geology 21, 81–120.Google Scholar
  12. 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.Google Scholar
  13. Klitgord, K. D. and Mammerickx, J.: 1982, ‘Northern East Pacific Rise: Magnetic Anomaly and Bathymetric Framework’, J. Geophys. Res. 87, 6725–6750.Google Scholar
  14. Larson, R. L.: 1971, ‘Near-Bottom Geologic Studies of the East Pacific Rise Crest’, Geol. Soc. Amer. Bull. 82, 823–841.Google Scholar
  15. Lonsdale, P.: 1977, ‘Regional Shape and Tectonics of the Equatorial East Pacific Rise’, Mar. Geophys. Res. 3, 295–315.Google Scholar
  16. Lonsdale, P.: 1983, ‘Overlapping Rift Zones at the 5.5°S Offset of the East Pacific Rise’, J. Geophys. Res. 88, 9393–9406.Google Scholar
  17. Lonsdale, P.: 1985, ‘Linear Volcanoes along the Pacific-Cocos Plate Boundary, 9°N to the Galapagos Triple Junction’, Tectonophysics 116, 255–279.Google Scholar
  18. 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.Google Scholar
  19. McKenzie, D. P. and Morgan, W. J.: 1969, ‘Evolution of Triple Junctions’, Nature 224, 125–133.Google Scholar
  20. Neprochnov, Y. P., Sedov, V. V., Semenov, G. A., Yel'Nikov, I. N., and Filaktov, V. D.: 1980, ‘The Crustal Structure and Seismicity of the Hess Basin Area in the Pacific Ocean’, Oceanology 20, 317–322.Google Scholar
  21. Normark, W. R.: 1976, ‘Delineation of the Main Extrusion Zone of the East Pacific Rise’, Geology 4, 681–685.Google Scholar
  22. Patriat, P. and Courtillot, V.: 1984, ‘On the Stability of Triple Junctions and its Relation to Episodicity in Spreading’, Tectonics 3, 317–332.Google Scholar
  23. Renard, V. and Allenou, J-P.: 1979, ‘SEABEAM, Multi-Beam Echo-Sounding in “Jean Charcot”. Description, Evaluation and First Results’, Int. Hydr. Rev. 56, 35–67.Google Scholar
  24. RISE Scientific Team: 1979, ‘The Tamayo Transform: Insight into the Tectonic Behaviour of Ridge/Ridge Transform Plate Boundaries. AGU Spring Meeting, EOS, Trans. Amer. Geophys. Union, 60, 376, abstract.Google Scholar
  25. Searle, R.: 1980, ‘Tectonic Pattern of the Azores Spreading Centre and Triple Junction’, Earth Planet. Sci. Lett. 51, 415–434.Google Scholar
  26. Searle, R.: 1984, ‘GLORIA Survey of the East Pacific Rise near 3.5°S: Tectonic and Volcanic Characteristics of a Fast-Spreading Mid-Ocean Rise’, Tectonophysics 101, 319–344.Google Scholar
  27. 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.Google Scholar
  28. Searle, R. C. and Laughton, A. S.: 1981, ‘Fine-Scale Sonar Study of Tectonics and Volcanism on the Reykjanes Ridge’, Proc. 26th Int. Geol. Congress, Geology of Oceans Symposium, Paris, 7–17 July 1980. Oceanologica Acta, suppl. to Vol. 4, pp. 5–13.Google Scholar
  29. Sleep, N. H. and Rosendahl, B. R.: 1979, ‘Topography and Tectonics of Mid-Oceanic Ridge Axes’, J. Geophys. Res. 84, 6831–6839.Google Scholar
  30. 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, Proc. IEEE/IERE sub-conf. on offshore instrumentation and communications. Oceanology International, 1978, Tech. session J, pp. 16–24, BPS Publications Ltd., London.Google Scholar
  31. Vening-Meinesz, F. A.: 1950, ‘Les graben africains, resultat de compression ou de tension dans la croute terrestre?’ Inst. roy. colonial belge, Bull. 21, 539–552.Google Scholar
  32. Zhivago, A. V.: 1979, ‘The Morphostructure of the Seafloor in the Southeastern Part of the Pacific Ocean’, in Metallonosnyye osadki yugo-vostochnoy chasti Tikhogo okeana (Metalliferous sediments of the southeastern Pacific), Moscow, Nauka, 1979.Google Scholar
  33. Zonenshain, L. P., Kogan, L. I., Savostin, L. A., Golmstock, A. J., and Gorodnitskii, A. M.: 1980, ‘Tectonics, Crustal Structure, and Evolution of the Galapagos Triple Junction’, Mar. Geology 37, 209–230.Google Scholar

Copyright information

© D. Reidel Publishing Company 1986

Authors and Affiliations

  • R. C. Searle
    • 1
  • J. Francheteau
    • 2
  1. 1.Institute of Oceanographic SciencesGodalmingUnited Kingdom
  2. 2.Institut de Physique du GlobeParisFrance

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