Marine Geophysical Researches

, Volume 18, Issue 1, pp 13–52 | Cite as

Abundant seamounts of the Rano Rahi seamount field near the Southern East Pacific Rise, 15° S to 19° S

  • Daniel S. Scheirer
  • Ken C. Macdonald
  • Donald W. Forsyth
  • Yang Shen


A widespread seamount province, the Rano Rahi Field, is located near the superfast spreading Southern East Pacific Rise (SEPR) between 15°–19° S. Particularly abundant volcanic edifices are found on Pacific Plate aged 0 to ∼ 6.5 Ma between 17°–19° S, an area greater than 100,000 km2. The numbers of seamounts and their volume are several times greater than those of a comparablysurveyed area near the Northern East Pacific Rise (NEPR), 8°–17° N. Most of the Rano Rahi seamounts belong to chains, which vary in length from ∼ 25 km to >240 km and which are very nearly collinear with the Pacific absolute and relative plate motion directions. Bends of 10°–15° occur along a few of the chains, and some adjacent chains converge or diverge slightly. Many seamount chains have fluctuations in volume along their length, and statistical tests suggest that some adjacent chains trade-off in volume. Several seamount chains split into two lines of volcanoes approaching the axis. In general, seamount chains composed of individual circular volcanoes are found near the axis; the chains consist of variably-overlapping edifices in the central part of the survey; to the west, volcanic ridges predominate. Near the SEPR, the volume of nearaxis seamount edifices is generally reduced near areas of deflated cross-sectional area of the axial ridge. Fresh lava flows, as imaged by sidescan sonar and sampled by dredging, exist around some seamounts throughout the entire survey area, in sharp contrast to the absence of fresh flows beyond ∼ 30 km from the NEPR. Also, the increases in seamount abundance and volume extend to much greater crustal ages than near the NEPR. Seamount magnetization analysis is also consistent with this wider zone of seamount growth, and it demonstrates the asynchronous formation of most of the seamount chains and volcanic ridges. The variety of observations of the SEPR seamounts suggests that a number of factors and mechanisms might bring about their formation, including the mantle upwelling associated with superfast spreading, off-axis mantle heterogeneities, miniplumes and local upwelling, and the vulnerability of the lithosphere to penetration by volumes of magma. In particular, we note the association of extensive, recent volcanism with intermediate wavelength gravity lineaments lows on crust aged ∼ 6 Ma. This suggests that the lineaments and some of the seamounts share a common cause which may be related to ridge-perpendicular asthenospheric convection and/or some manner of extension in the lithosphere.

Key words

East Pacific rise seamounts seafloor volcanism MELT 


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  1. Abers, G. A., Parsons, B., and Weissel, J. K., 1988, Seamount abundances and distributions in the southeast Pacific, Earth Planet. Sci. Lett. 87, 137–151.Google Scholar
  2. Barone, A. and Ryan, W. B. F., 1990, Single plume model for asynchronous formation of the Lamont seamounts and adjacent East Pacific Rise terrain, J. Geophys. Res. 95, 10801–10827.Google Scholar
  3. Barr, S. M., 1974, Seamount chains formed near the crest of Juan de Fuca Ridge, northeast Pacific Ocean, Mar. Geol. 17, 1–19.Google Scholar
  4. Bemis, K. G. and Smith, D. K., 1993, Production of small volcanoes in the Superswell region of the South Pacific, Earth Planet. Sci. Lett. 118, 251–263.Google Scholar
  5. Buck, W. R. and Parmentier, E. M., 1986, Convection beneath young oceanic lithosphere: Implications for thermal structure and gravity, J. Geophys. Res. 91, 1961–1974.Google Scholar
  6. Clague, D. A. and Dalrymple, G. B., 1989, Tectonics, geochemistry, and origin of the Hawaiian-Emperor volcanic chain, in The Geology of North America, Winterer, E. L., Hussong, D. M., and Decker, R. W. (eds.), Geological Society of America, Boulder, Colorado, pp. 188–217.Google Scholar
  7. Cochran, J. R., 1986, Variation in subsidence rates along intermediate and fast spreading mid-ocean ridges, Geophys. J. R. Astron. Soc. 87, 421–454.Google Scholar
  8. Cormier, M.-H. and Macdonald, K. C., 1994, East Pacific Rise 18°–19°S: Asymmetric spreading and ridge reorientation by ultrafast migration of axial discontinuities, J. Geophys. Res. 99, 543–564.Google Scholar
  9. Cormier, M.-H., Scheirer, D. S., and Macdonald, K. C., 1996, Evolution of the East Pacific Rise at 16°–19° S since 5 Ma: Bisection of Overlapping Spreading Centers by New, Rapidly Propagating Ridge Segments, Mar. Geophys. Res. 18, 53–84 (this issue).Google Scholar
  10. Davis, E. E. and Karsten, J. L., 1986, On the cause of the asymmetric distribution of seamounts about the Juan de Fuca Ridge: Ridgecrest migration over a heterogeneous asthenosphere, Earth Planet. Sci. Lett. 79, 385–396.Google Scholar
  11. Dekov, V. M. and Kupstov, V. M., 1990, Rates of accumulation of metal-bearing sediments on the East Pacific Rise (20° S), Oceanology 30, 321–324.Google Scholar
  12. Dekov, V. M. and Kuptsov, V. M., 1992, Late Quaternary rates of accumulation of metal-bearing sediments on the East Pacific Rise, Oceanology 32, 94–101.Google Scholar
  13. DeMets, C., Gordon, R. G., Argus, D. F., and Stein, S., 1990, Current plate motions, Geophys. J. Int. 101, 425–478.Google Scholar
  14. Desonie, D. L. and Duncan, R. A., 1990, The Cobb-Eikelberg seamount chain: Hotspot volcanism with mid-ocean ridge basalt affinity, J. Geophys. Res. 95, 12697–12711.Google Scholar
  15. Detrick, R. S., Buhl, P., Vera, E., Mutter, J., Orcutt, J., Madsen, J., and Brocher, T., 1987, Multi-channel seismic imaging of a crustal magma chamber along the East Pacific Rise, Nature 326, 35–41.Google Scholar
  16. Detrick, R. S., Harding, A. J., Kent, G. M., Orcutt, J. A., Mutter, J. C., and Buhl, P., 1993, Seismic structure of the southern East Pacific Rise, Science 259, 499–503.Google Scholar
  17. Dunbar, J. and Sandwell, D. T., 1988, A boudinage model for crossgrain lineations, EOS Trans. AGU 69, 1429.Google Scholar
  18. Edwards, M. H., Fornari, D. J., Malinverno, A., Ryan, W. B. F., and Madsen, J., 1991, The regional tectonic fabric of the East Pacific Rise from 12° 50'N to 15° 10'N, J. Geophys. Res. 96, 7995–8017.Google Scholar
  19. Goodwillie, A. M. and Parsons, B., 1992, Placing bounds on lithospheric deformation in the central Pacific Ocean, Earth Planet. Sci. 111, 123–139.Google Scholar
  20. Gripp, A. E. and Gordon, R. G., 1990, Current plate velocities relative to the hotspots incorporating the NUVEL-1 plate motion model, Geophys. Res. Lett. 17, 1109–1112.Google Scholar
  21. Gurnis, M., 1986, Stirring and mixing in the mantle by plate-tectonic flow: Large persistent blobs and long tendrils coexist, Geophys. Res. Lett. 13, 1464–1467.Google Scholar
  22. Haxby, W. F. and Weissel, J. K., 1986, Evidence for small-scale convection from Seasat altimeter data, J. Geophys. Res. 91, 3507–3520.Google Scholar
  23. Jordan, T. H., Menard, H. W., and Smith, D. K., 1983, Density and size distribution of seamounts in the eastern Pacific inferred from wide-beam sounding data, J. Geophys. Res. 88, 10508–10518.Google Scholar
  24. Kellogg, L. H. and Turcotte, D. L., 1990, Mixing and the distribution of heterogeneities in a chaotically convecting mantle. J. Geophys. Res. 95, 421–432.Google Scholar
  25. Kleinrock, M. C., Brooks, B. A., and Smith, D. K., 1994, Construction and destruction of volcanic knobs at the Cocos-Nazca spreading system near 95° W, Geophys. Res. Lett. 21, 2307–2310.Google Scholar
  26. Lonsdale, P., 1989, Segmentation of the Pacific-Nazca spreading center, 1° N-20° S, J. Geophys. Res. 94, 12197–12226.Google Scholar
  27. Lyle, M., Leinen, M., Owen, R. M., and Rea, D. K., 1987, Late Tertiary history of hydrothermal deposition at the East Pacific Rise, 19°S: correlation to volcano-tectonic events, Geophys. Res. Lett. 14, 595–598.Google Scholar
  28. Macdonald, K. C., Fox, P. J., Miller, S., Carbotte, S., Edwards, M. H., Eisen, M., Fornari, D. J., Perram, L., Pockalny, R., Scheirer, D., Tighe, S., Weiland, C., and Wilson, D., 1992, The East Pacific Rise and its flanks 8°–18° N: History of segmentation, propagation and spreading direction based on SeaMARCII and Sea Beam studies, Mar. Geophys. Res. 14, 299–344.Google Scholar
  29. Mahoney, J. J., Sinton, J. M., Kurz, M. D., Macdougall, J. D., Spencer, K. J., and Lugmair, G. W., 1994, Isotope and trace element characteristics of a superfast spreading ridge: East Pacific Rise, 13°–23° S, Earth Planet. Sci. Lett. 121, 173–193.Google Scholar
  30. Mammerickx, J., Anderson, R. N., Menard, H. W., and Smith, S. M., 1975, Morphology and tectonic evolution of the east central Pacific, Geol. Soc. Am. Bull. 86, 111–118.Google Scholar
  31. Marchig, V., Erzinger, J., and Heinze, P. M., 1986, Sediments in the black smoker area of the East Pacific Rise (18.5° S), Earth Planet. Sci. Lett. 79, 93–106.Google Scholar
  32. McNutt, M. K. and Fischer, K. M., 1987, The South Pacific superswell, in Seamounts, Islands, and Atolls, Keating, B. H., Fryer, P., Batiza, R., and Boehlerg, G. W. (eds.), Geophysical Monograph 43, American Geophysical Union, Washington, D.C., pp. 25–34.Google Scholar
  33. McNutt, M. K. and Judge, A. V., 1990, The superswell and mantle dynamics beneath the South Pacific, Science 248, 969–975.Google Scholar
  34. Menard, H. W.: 1964, [Marine Geology of the Pacific], McGraw Hill, New York.Google Scholar
  35. Moore, J. G., Normark, W. R., and Holcomb, R. T., 1994, Giant Hawaiian Landslides, Ann. Rev. Earth Planet. Sci. 22, 119–144.Google Scholar
  36. Naar, D. F. and Hey, R. N., 1989, Recent Pacific-Easter-Nazca plate motions, in Evolution of Mid-Ocean Ridges, Sinton, J. M. (ed.), IUGG Geophysical Monograph 57, pp. 9–30.Google Scholar
  37. Parsons, B. and McKenzie, D., 1978, Mantle convection and the thermal structure of plates, J. Geophys. Res. 83, 4485–4496.Google Scholar
  38. Perram, L. J., Cormier, M.-H., and Macdonald, K. C., 1993, Magnetic and tectonic studies of the duelling propagating spreading centers at 20° 40' S on the East Pacific Rise: Evidence for crustal rotations, J. Geophys. Res. 98, 13835–13850.Google Scholar
  39. Renard, V., Hekinian, R., Francheteau, J., Ballard, R. D., and Bäcker, H., 1985, Submersible observations at the axis of the ultra-fast spreading East Pacific Rise (17° 30' S to 21° 30'S), Earth Planet. Sci. Lett. 75, 339–353.Google Scholar
  40. Richter, F. M. and Daley, S. F., 1989, Dynamical and chemical effects of melting a heterogeneous source, J. Geophys. Res. 94, 12499–12510.Google Scholar
  41. Sandwell, D. T. and Dunbar, J., 1988, Stretching of the central Pacific lithosphere: Super swell, crossgrain lineations and en-echelon ridges, EOS Trans. AGU 69, 1429.Google Scholar
  42. Sandwell, D. T., Winterer, E. L., Mammerickx, J., Duncan, R. A., Lynch, M. A., Levitt, D., and Johnson, C. L., submitted, Evidence foom the Pukapuka Ridges for diffuse extension of the Pacific Plate: No mini hotspots, no convection, J. Geophys. Res. Google Scholar
  43. Scheirer, D. S., Forsyth, D. W., and Macdonald, K. C., in prep., The development of lineaments in the gravity field near the Southern East Pacific Rise.Google Scholar
  44. Scheirer, D. S. and Macdonald, K. C., 1993, Variation in cross-sectional area of the axial ridge along the East Pacific Rise: Evidence for the magmatic budget of a fast spreading center, J. Geophys. Res. 98, 7871–7885.Google Scholar
  45. Scheirer, D. S. and Macdonald, K. C., 1995, Near-axis seamounts on the flanks of the East Pacific Rise, 8° N to 17° N, J. Geophys. Res. 100, 2239–2259.Google Scholar
  46. Scheirer, D. S., Macdonald, K. C., Forsyth, D. W., and the Gloria Legs 2 and 3 Scientific Parties, 1993, An extensive seamount field near the Southern East Pacific Rise 15° to 19° S, Eos Trans. AGU, Spring Meeting suppl. 73, (16), 297.Google Scholar
  47. Scheirer, D. S., Macdonald, K. C., Forsyth, D. W., Miller, S. P., Wright, D. J., Cormier, M.-H., and Weiland, C. M., this issue, A map series of the southern East Pacific Rise and its flanks, 15°–19° S, Mar. Geophys. Res. Google Scholar
  48. Scheirer, D. S., Macdonald, K. C., Forsyth, D. W., and the Gloria 2 and 3 Scientific Parties, 1993, Wide-spread volcanic and tectonic activity on the Southern East Pacific Rise and its flanks, Ridge Newsletter 4, 1–2, 8–10.Google Scholar
  49. Shen, Y., Forsyth, D. W., Scheirer, D. S., and Macdonald, K. C., 1993, Two forms of volcanism: implications for mantle flow and off-axis crustal production on the west flank of the southern East Pacific Rise, J. Geophys. Res. 98, 17875–17889.Google Scholar
  50. Shen, Y., Scheirer, D. S., Forsyth, D. W., and Macdonald, K. C., 1995, Trade-off in production of adjacent seamount chains near the East Pacific Rise, Nature 373, 140–143.Google Scholar
  51. Sinton, J. M., Hall, L. S., and Batiza, R., 1993, Geochemistry of the Rano Rahi Seamounts: mantle melting within 450 km of the East Pacific Rise, 15.5–19° S, EOS Trans. AGU, 74, Fall Meeting Supplement, 687.Google Scholar
  52. Sinton, J. M., Smaglik, S. M., Mahoney, J. J., and Macdonald, K. C., 1991, Magmatic processes at superfast spreading mid-ocean ridges: glass compositional variation along the East Pacific Rise 13°–23° S, J. Geophys. Res. 96, 6133–6155.Google Scholar
  53. Sleep, N. H., 1984, Tapping of magmas from ubiquitous mantle heterogeneities: an alternative to mantle plumes?, J. Geophys. Res. 89, 10029–10041.Google Scholar
  54. Smith, D. K., 1988, Shape analysis of Pacific seamounts, Earth Planet. Sci. Lett. 90, 457–466.Google Scholar
  55. Smith, D. K. and Cann, J. R., 1992, The role of seamount volcanism in crustal construction at the Mid-Atlantic Ridge (24°–30° N), J. Geophys. Res. 97, 1645–1658.Google Scholar
  56. Smith, D. K. and Jordan, T. H., 1987, The size distribution of Pacific seamounts, Geophys. Res. Lett. 14, 1119–1122.Google Scholar
  57. ten Brink, U., 1991, Volcano spacing and plate rigidity, Geology 19, 397–400.Google Scholar
  58. Trial, A. F. and Spera, F. J., 1990, Mechanisms for the generation of compositional heterogeneities in magma chambers, G.S.A. Bull. 102, 353–367.Google Scholar
  59. Wilson, D. S., 1992, Focused mantle upwelling beneath mid-ocean ridges: Evidence from seamount formation and isostatic compensation of topography, Earth Planet. Sci. Lett. 113, 41–55.Google Scholar
  60. Winterer, E. L. and Sandwell, D. T., 1987, Evidence from en-echelon crossgrain ridges for tensional cracks in the Pacific plate, Nature 329, 534–537.Google Scholar
  61. Zindler, A., Staudigel, H., and Batiza, R., 1984, Isotopic and trace element geochemistry of young Pacific seamounts: implications for the scale of upper mantle heterogeneity, Earth Planet. Sci. Lett. 70, 175–195.Google Scholar

Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • Daniel S. Scheirer
    • 1
  • Ken C. Macdonald
    • 1
  • Donald W. Forsyth
    • 2
  • Yang Shen
    • 2
  1. 1.Department of Geological SciencesUCSBSanta BarbaraUSA
  2. 2.Department of Geological SciencesBrown UniversityProvidenceUSA

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