Advertisement

A Geophysical Comparison between Fast and Slow Spreading Centers: Constraints on Magma Chamber Formation and Hydrothermal Activity

  • Ken C. Macdonald
Chapter
Part of the NATO Conference Series book series (NATOCS, volume 12)

Abstract

While there are many similarities in the geologic structure of various spreading centers, there are some important differences which appear to be related to spreading rate. Taking recent studies of the fast-spreading East Pacific Rise and slow-spreading Mid-Atlantic Ridge, I have compiled a list of properties (summarized in Table 1) which distinguish the two spreading centers. These studies include seismic reflection and refraction, microearthquake studies, gravity and magnetic measurements, electromagnetic sounding, thermal models, observations of hydrothermal activity and geomorphic/tectonic studies. For each of the contrasting properties listed in Table 1, I briefly explain in the text the origin of the observation and emphasize possible limitations and areas of disagreement in the associated interpretation. Many of the important contrasts between fast and slow spreading centers are related to the increased thermal budget at fast spreading rates which allows for the maintenance of a steady state chamber along most of the length of the rise. At slow spreading rates, the axial magma chamber may persist at distances greater than 15–20 km from transform fault intersections, but given the finite width and spacing of transform faults on slow spreading centers, the axial magma chamber may be transient along most of the ridge’s length. The mechanics and deformation of the lithosphere are also affected by the thermal budget as manifested by along strike topographic continuity, transform fault spacing and style of deformation along spreading center offsets. High temperature vents (350°C) are common at intermediate to fast spreading rates, but may be rare occurrences at slow speading rates (with the possible exception of the Reykjanes ridge and other hot-spot influenced ridges). At most slow-spreading ridges, the frequency and duration of such hydrothermal events may not be adequate to sustain the chemosynthetic benthic faunal communities which thrive on faster spreading centers.

Keywords

Magma Chamber Spreading Rate Spreading Center Seismic Refraction East Pacific Rise 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Anderson, R. N., Langseth, M. G., and Sclater, J. G., 1977, The mechanisms of heat transfer through the floor of the Indian Ocean, J. Geophys. Res., 82: 3391–3409.CrossRefGoogle Scholar
  2. Atwater, T. M., 1979, Constraints from the Famous area concerning the structure of the oceanic section. Deep drilling results in the Atlantic Ocean: Ocean crust. Eds. M. Talwani, C. G. Harrison, and D. E. Hayes, 2: 33–42.Google Scholar
  3. Atwater, T. M., and Mudie, J. D., 1973, Detailed near-bottom geophysical study of the Gorda Rise, J. Geophys, Res., 78: 8665–8686.CrossRefGoogle Scholar
  4. Ballard, R. D., Francheteau, J., Juteau, T., Rangan, C. and Normark, W., 1981, East Pacific Rise at 21°N: The volcanic, tectonic and hydrothermal processes of the central axis, Earth. Planet. Sci. Lett., 55: 1–10.CrossRefGoogle Scholar
  5. Becker, K., and Von Herzen, R. P., 1982, Heat transfer through the sediments of the mounds hydrothermal area, Galapagos Spreading Center at 86 W, EOS, 63: 529–536.Google Scholar
  6. Becker, K., Von Herzen, R. P., Francis, R. J. G., Anderson, R. N., Honnorez, J., Adamson, A. C., Alt, J. C., Emmerman, R., Kempton, P. D., Kinoshita, H., Laverne, C., Mohl, M. J., and Newmark, R. L., In situ electrical resistivity and bulk porosity of the ocean crust; Costa Rica Rift, Nature, in press, 1982.Google Scholar
  7. Bibee, L. D., 1979, Crustal structure in areas of active crustal accretion, Ph. D. Thesis, University of California, San Diego, pp. 155.Google Scholar
  8. Blakely, R. J., and Lynn, W. S., 1977, Reversal transition widths and fast spreading centers, Earth Planet. Sci. Lett., 33: 321–330.CrossRefGoogle Scholar
  9. Bryan, W. B., and Moore, J. G., 1977, Compositional variations of young basalts in the Mid-Atlantic Ridge rift valley near lat. 36°49’N, Geol. Soc. Amer. Bull., 88: 556–570.CrossRefGoogle Scholar
  10. Bryan, W. B., G. Thompson, and P. J. Michael, 1979, Compositional variation in a steady-state zoned magma chamber: Mid-Atlantic Ridge at 36°50 N, Tectonophysics, 55: 63–85.CrossRefGoogle Scholar
  11. Cande, S. C., and Kent, D. V., 1976, Constraints imposed by the shape of marine magnetic anomalies on the magnetic source, J. Geophys. Res., 81: 4157–4162.CrossRefGoogle Scholar
  12. Cochran, J. R., 1979, An analysis of isostacy in the world’s oceans, part 2, mid ocean ridge crests, J. Geophys. Res., 84: 4713–4729.CrossRefGoogle Scholar
  13. 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, Tj. H., 1979, Submarine thermal springs on the Galapagos Rift, Science 203: 1073–1083.Google Scholar
  14. Converse, D. R., Holland, H. D., and Edmond, J. M., 1982, Hydrothermal flow rates at 21°N, EOS, 63: 472.Google Scholar
  15. CYAMEX Team, 1980, First manned submersible dives on the East Pacific Rise at 21°N (Project RITA): General Results, Mar. Geophys. Res., 4: 345–379.CrossRefGoogle Scholar
  16. Dewey, J. F., Kidd, W. S. F., 1977, Geometry of plate accretion, Geol. Soc. Amer. Bull., 88: 960–968.CrossRefGoogle Scholar
  17. Edmond, J. M., 1980, The chemistry of the 350°C hot springs at 21°N on the East Pacific Rise, EOS 61: 992.CrossRefGoogle Scholar
  18. Elder, J. W., 1965, Physical processes in geothermal areas. In: Terrestrial Heat Flow Am. Geophys. Union Monogr., 8: 211–239.Google Scholar
  19. Fehn, U., Siegel, M. D., Robinson, G. R., Holland, H. D., Williams, D. L., Erickson, A. J., Green, K. E., 1977, Deep-water temperatures in the Famous area, Geol. Soc. Amer. Bull. 88: 488–494.CrossRefGoogle Scholar
  20. Finkel, R. C., MacDougall, J. D., Chung, Y. C., 1980 Sulfide precipitates at 21°N on the East Pacific Rise: ‘26Ra, 210Pb and 210Po, Geophys. Res. Lett., 7: 685–688.CrossRefGoogle Scholar
  21. Fowler, C. M. R., 1976, Crustal structure of the Mid-Atlantic Ridge crest at 37°N, Geophys. J. Roy. Astr. Sop., 47: 459–491.CrossRefGoogle Scholar
  22. Fox, P. J., and Stroup, J. B., 1981, The plutonic foundation of the oceanic crust, The Sea, 7: 119–218.Google Scholar
  23. Francheteau, J., and Ballard, R. D., 1982, The East Pacific Rise near 21°N, 13°N and 20°S: Inferences for along-strike variability of axial processes at the Mid-Ocean Ridge, Earth Planet Sci. Lett., in press.Google Scholar
  24. Francis, T. J. G., and Porter, I. T., 1973, Median valley seismology: The Mid-Atlantic Ridge near 45°N, Geophys. J. Roy. Astr. Soc., 34: 279–311.CrossRefGoogle Scholar
  25. Francis, T. J. G., Porter, I. T., and McGrath, J. R., 1977, Ocean bottom seismograph observations on the Mid-Atlantic Ridge near 37°N, Geol. Soc. Am. Bull., 88: 664–677.CrossRefGoogle Scholar
  26. Green, K. E., 1980, Geothermal processes at the Galapagos Spreading Center, Ph.D. Dissertation, WHOI-80–33.Google Scholar
  27. Green, K. E., Von Herzen, R. P., Williams, D. L., 1981, The Galapagos Spreading Center at 86°W: A detailed geothermal field study, J. Geopys. Res., 86: 979–986.CrossRefGoogle Scholar
  28. Hale, L. D., Morton, C. J., and Sleep, N. H., 1982, Reinterpretation of seismic reflection data over the East Pacific Rise, J. Geophys. Res., 87: 7707–7719.CrossRefGoogle Scholar
  29. Hall, J. M., 1976, Major problems regarding the magnetization of oceanic crustal layer 2, J. Geooys. Res., 81: 4223–4230.Google Scholar
  30. Harrison, C. G. A., 1968, Formation of magnetic anomaly patterns by dyke injection, J. Geophys. Res., 73: 2137–2142.CrossRefGoogle Scholar
  31. Harrison, C. G. A., 1981, Magnetism of the oceanic crust, The Sea, 7: 219–237.Google Scholar
  32. Haymon, R., and Kastner, M., 1981, Hot spring deposits on the East Pacific Rise at 21°N: preliminary description of mineralogy and genesis, Earth Planet. Sci. Lett., 53: 363–381.CrossRefGoogle Scholar
  33. Herron, T. J., Stoffa, P. L., and Buhl, P., 1980, Magma chamber and mantle reflections–East Pacific Rise, Geophys. Res. Lett., 7: 989–992.CrossRefGoogle Scholar
  34. Hey, R., Duennebier, F. K., and Morgan, W. J., 1980, Propagating rifts on mid-ocean ridges, J. Geophys. Res., 85: 3647–3658.CrossRefGoogle Scholar
  35. Johnson, H. P., Karsten, J. L., Delaney, J. R., Davis, E. E., Currie, R. G., and Chase, R. L., A detailed study of the Cobb offset of the Juan de Fuca Ridge: Evolution of a propagating rift, J. Geophys. Res., in press.Google Scholar
  36. Jung, H., and Lewis, B. T. R., 1982, Seismic refraction results from the southern Juan de Fuca Ridge, EOS, 63: 1153.Google Scholar
  37. Keen, C. E., and Tramontini, C., 1970, A seismic refraction survey on the Mid-Atlantic Ridge, Geophys. J. Roy. Astr. Soc., 20: 473–491.CrossRefGoogle Scholar
  38. Kidd, R. G. W., 1977, A model for the process of formation of upper oceanic crust, Geophvs. J. Roy. Astr. Soc., 50: 149–183.CrossRefGoogle Scholar
  39. Killingley, J. S., Berger, W. H., Macdonald, K. C., and Newman, W. A., 1980, 180/160 variations in deep sea carbonate shells from the RISE hydrothermal field, Nature, 288: 218, 221.Google Scholar
  40. Klitgord, K. D., Huestis, S. P., Parker, R. L., and Mudie, J. D., 1975, An analysis of near-bottom magnetic anomalies: Sea floor spreading, the magnetized layer, and the geomagnetic time scale, Geophys. J. Roy. Astr. Soc., 43: 387–424.CrossRefGoogle Scholar
  41. Lachenbruch, A. H., 1973, A simple mechanical model for oceanic spreading centers, J. Geophys. Res., 78: 3395–3417.CrossRefGoogle Scholar
  42. Lewis, B. T. R., 1982, Constraints on the structure of the East Pacific Rise from gravity, J. Geophys. Res., 87: 8491–8500.CrossRefGoogle Scholar
  43. Lilwall, R. C., Francis, T. J. G., and Porter, I. T., 1978, Ocean bottom seismograph observations on the Mid-Atlantic Ridge near 45°N–further results, Geophys. J. Roy. Astr. Soc., 55: 255–262.CrossRefGoogle Scholar
  44. Lister, C. R. B., 1972, On the thermal balance of a mid-ocean ridge, Geophys. J. Roy. Astr. Soc., 26: 515–535.CrossRefGoogle Scholar
  45. Lister, C. R. B., 1977, Qualitative models of spreading center processes, including hydrothermal penetration, Tectonophysics, 37: 203–218.Google Scholar
  46. Lister, C. R. B., 1982, On the intermittency of seafloor spreading, EOS, 63: 1153.Google Scholar
  47. Lonsdale, P., 1977 Structural geomorphology of a fast-spreading rise crest: The East Pacific Rise near 3°25’S, Mar. Geophys..., 3:251–293.Google Scholar
  48. Lonsdale, P., 1982, Small offsets of the Pacific-Nazca and Pacific-Cocos spreading axes, EOS, 63: 1108.Google Scholar
  49. Macdonald, K. C., 1977, Near-bottom magnetic anomalies, asymmetric spreading, oblique spreading and tectonics of the Mid-Atlantic Ridge near 37°N, Geol. Soc. Am. Bull., 88: 541–555.CrossRefGoogle Scholar
  50. Macdonald, K. C., 1982, Mid-ocean ridges: Fine-scale tectonic, volcanic and hydrothermal processes within the plate boundary zone, Ann. Rev. Earth Planet. Sci., 10: 155–190.CrossRefGoogle Scholar
  51. Macdonald, K. C., Miller, S. P., Huestis, S. P., and Spiess, F. N., 1980a, Three-dimensional modeling of a magnetic reversal boundary from inversion of deep-tow measurements, J. Geophys. Res., 85: 3670–3680.CrossRefGoogle Scholar
  52. Macdonald, K. C., Becker, F., Spiess, F. N., and Ballard, R. D., 1980b, Hydrothermal heat flux of the “black smoker” vents on the East Pacific Rise, Earth Planet, Sci. Lett. j$: 1–7.Google Scholar
  53. Macdonald, Ken C., and Fox, P. J., 1983, Overlapping spreading centers: new accretion geometry on the East Pacific Rise, Nature, 302: 55–58.CrossRefGoogle Scholar
  54. Macdonald, K. C., Kastens, K., Spiess, F. N., and Miller, S. P., 1979, Deep tow studies in the Tamayo Transform Fault, Marine Geophys. Res., 4: 37–70.CrossRefGoogle Scholar
  55. Macdonald, K. C., and Luyendyk, B. P., 1977, Deep-tow studies of the structure of the Mid-Atlantic Ridge crest near lat. 37°N, Geol. Soc. Amer. Bull., 88, 621–636, 1977.Google Scholar
  56. Macdonald, K. C., Luyendyk, B. P., Mudie, J. D., and Spiess, F. N., 1975, Near-bottom geophysical study of the Mid-Atlantic Ridge median valley near lat. 37°N: Preliminary observations, Geology, 3: 211–215.CrossRefGoogle Scholar
  57. Macdonald, K. C., Miller, S. P., Luyendyk, B. P., Atwater, T. M., and Shure, L., Investigation of an Vine-Matthews magnetic lineation from a submersible: The source and character of marine magnetic anomalies, J. Geophys. Res., in press.Google Scholar
  58. Macdonald, K. C., and Mudie, J. D., 1974, Microearthquakes on the Galapagos Spreading Center and the seismicity of fast-spreading ridges, Geophys. J. R. Astr. Soc,, 36: 245–257.CrossRefGoogle Scholar
  59. Malahoff, A., 1982, Massive enriched polymetallic sulfides of the ocean floor - a new commercial source of strategic minerals? OTC 4293.Google Scholar
  60. Matthews, D. H., and Bath, J. 1967. Formation of magnetic anomaly patterns on the Mid-Atlantic Ridge, Geophys. J. Roy. Astr. soc., 13: 349–357.CrossRefGoogle Scholar
  61. Mammerickx, J., and Smith, S. M., 1978, Bathymetry of the Southeast Pacific, Geol. Soc. Amer., Map and Chart Series MC-26.Google Scholar
  62. McClain, J. S., and Lewis, B. T. R., 1980, A seismic experiment of the axis of the East Pacific Rise, Marine Geol., 35: 147–169.CrossRefGoogle Scholar
  63. Menard, H. W., 1967, Seafloor spreading, topography and second layer, Science, 157: 923–924.CrossRefGoogle Scholar
  64. Morton, J. L., Tompkins, D. H., Normark, W. R., and Sleep, N. H., 1982, Structure of the southern Juan de Fuca ridge from multi-channel seismic reflection records, EOS, 63: 1153.Google Scholar
  65. Nisbet, E. G., ad Fowler, C. M. R., 1978, The Mid-Atlantic Ridge at 37°and 45°N, some geophysical and petrologic constraints, Geophys. J. Roy. Astr. Soc., 54: 631–660.CrossRefGoogle Scholar
  66. Normark, W. R., Morton, J. L., and Delaney, J. R., 1982, Geologic setting of massive sulfide deposits and hydrothermal vents along the southern Juan de Fuca Ridge, USGS, open-file report 82–200A.Google Scholar
  67. Orcutt, J. A., Kennett, B. L. N., and Dorman, L. M., 1976, Structure of the East Pacific Rise from an ocean bottom seismometer array, Geophys. J. Roy. Astr. Soc., 45: 305–320.CrossRefGoogle Scholar
  68. Orcutt, J. A., McClain, J. S., Burnett, M., Seismic constraints on the generation, evolution and structure of the ocean crust, Geol. Soc. of London Spec. Pub., in press.Google Scholar
  69. Pallister, J. S., and Hopson, C. A., 1981, Semail ophiolite plutonic suite: Field relations, phase variations, cryptic variation and layering, and a model of a spreading ridge magma chamber, J. Geopys. Res., 79: 1587–1593.Google Scholar
  70. Parker, R. L., and Huestis, S. P., 1974, The inversion of magnetic anomalies in the presence of topography, J. Geonys. Res., 79: 1587–1593.CrossRefGoogle Scholar
  71. Parker, R. L., and Oldenburg, D. W., 1973, Thermal model of ocean ridges, Nature Phys. Sei., 242: 137–139.CrossRefGoogle Scholar
  72. Poehls, K., 1974, Seismic refraction on the Mid-Atlantic Ridge at 37°N, J. Geophys. Res., 79: 3370–3373.CrossRefGoogle Scholar
  73. Prothero, W., and Reid, I., 1982, Microearthquake results from the East Pacific Rise, J. Geon ys. Res., 87: 8509–8518.CrossRefGoogle Scholar
  74. Purdy, G. M., Detrick, R. S., and Cormier, M., 1982, Seismic constraints on the crustal structure at a ridge-fracture zone intersection, EOS, 63: 1100.Google Scholar
  75. Ramberg, I. B., Gray, D. F., and Raynolds, R. G. H., 1977, Tectonic evolution of the FAMOUS area of the Mid-Atlantic Ridge, lat. 35 50’ to 37 20’N, Geol. Soc. Amer. Bull., 88: 609–620.CrossRefGoogle Scholar
  76. Riedesel, M., Orcutt, J. A., Macdonald, K. C., and McClain, J. S., 1982, Microearthquakes in the Black Smoker Hydrothermal Field, East Pacific Rise at 21 ° N, 87: 10613–10624.Google Scholar
  77. Reid, I. D., and Macdonald, K. C., 1973, Microearthquake study of the Mid-Atlantic Ridge near 37°N using sonobuoys, Nature, 246: 88–90.CrossRefGoogle Scholar
  78. Reid, I. D., Orcutt, J. A., and Prothero, W. A., 1977, Seismic evidence for a narrow zone of partial melting underlying the East Pacific Rise at.2T°N, Geol. Soc. Amer. Bull., 88: 678–682.CrossRefGoogle Scholar
  79. RISE Team: Spiess, F. N., Macdonald, K. C., Atwater, T., Ballard, R., Carranza, A., Cordoba, D., Cox, C., Diaz Garcia, V. M., Francheteau, J., Guerrero, J., Hawkins, J., Haymon, R., Hessler, R., Juteau, T., Kastner, M., Larson, R., Luyendyk, B., MacDougall, J. D., Miller, S., Normark, W., Orcutt, J., and Rangin, C., 1980, East Pacific Rise: Hot springs and geophysical experiments, Science, 207: 1421–1433.Google Scholar
  80. Rona, P. A., 1980, TAG hydrothermal field: Mid-Atlantic Ridge Crest at latitude 26°N, J. Geol. Soc. London, 137: 385–402.CrossRefGoogle Scholar
  81. Rona, P. A., Bostrom, K., and Epstein, S., 1980, Hydrothermal quartz vug from the Mid-Atlantic Ridge, Geology, 8: 569–572.CrossRefGoogle Scholar
  82. Rosendahl, B. R., Raitt, R. W., Dorman, L. M., Bibee, L. D., Hussong, D. M., and Sutton, G. H., 1976, Evolution of oceanic crust, 1. A physical model of the East Pacific Rise crest derived from seismic refraction data, J. Geophys. Res., 81: 5294–5305.CrossRefGoogle Scholar
  83. Schouten, H., and Klitgord, K. D., 1982, The memory of the accreting plate boundary and the continuity of fracture zones,. Earth Planet Sci. Lett., 59: 255–266.CrossRefGoogle Scholar
  84. Schouten, H., Denham, C., and Smith, W., 1982, On the quality of marine magnetic anomaly sources and sea-floor topography, Geophys. J. Roy. Astr. Soc., 70: 245–260.CrossRefGoogle Scholar
  85. Sclater, J. G., and Francheteau, J., 1970, The implications of terrestrial heat flow observations on current tectonic and geochemical models of the crust and upper mantle of the Earth, Geophys. J. Roy. Astr. Soc., 20: 509–542.Google Scholar
  86. Simoneit, B. R. T., and Lonsdale, P. F., 1982, Hydrothermal petroleum on mineralized mounds at the seabed of Guaymas Basin, Nature, 295: 198–202.CrossRefGoogle Scholar
  87. Sleep, N. H., 1969, Sensitivity of heat flow and gravity to the mechanism of seafloor spreading, J. Geophys. Res., 74: 542–549.Google Scholar
  88. Sleep, N. H., 1975, Formation of ocean crust: Some thermal constraints, J. Geophys. Res., 80: 4037–4042.CrossRefGoogle Scholar
  89. Sleep, N. H., Hydrothermal convection at ridge axes, P. Rona et al., eds., Hydrothermal Processes at Spreading. Centers, Plenum, in press.Google Scholar
  90. Sleep, N. H., and Biehler, S., 1970, Topography and tectonics at the intersections of fracture zones with central rifts, J. Geophys. Res., 75: 2748–2752.CrossRefGoogle Scholar
  91. Sleep, N. H., Morton, J. L., Burns, L. E., Geophysical constraints on the volume of hydrothermal flow at ridge axes, P. Rona et al., eds., Hydrothermal Processes at Spreading Centers, Plenum, in press.Google Scholar
  92. Sleep, N. H., and Rosendahl, B. R., 1979, Topography and tectonics of mid-ocean ridge axes, J. Geophys. Res., 70: 341–352.Google Scholar
  93. Stakes, D., Shervais, J. W., and Hopson, C. A., The volcano-tectonic cycle of the FAMOUS and AMR valleys, Mid-Atlantic Ridge (36°47’N): Evidence from basalt glass and basalt phenocryst compositional variations for a steady-state magma chamber beneath the valley midsections, J. Geophys. Res., in press.Google Scholar
  94. Talwani, M., Le Pichon, X., and Ewing, M., 1965, Crustal structure of the mid-ocean ridges, J. Geophys. Res., 70: 341–352.CrossRefGoogle Scholar
  95. Tapponnier, P., and Francheteau, J., 1978, Necking of the lithosphere and the mechanics of slowly accreting plate boundaries, J. Geophys. Res., 83: 3955–3970.CrossRefGoogle Scholar
  96. Toomey, D. R., Murray, M. H., Purdy, G. M., Murray, M. H., 1982, Microearthquakes on the Mid-Atlantic Ridge near 23°N: new observations with a large network, EOS, 63: 1103.Google Scholar
  97. Trehu, A. M., and Solomon, S. C., 1981, Microearthquakes in the Orozco Fracture Zone: a closer look at the results from project ROSE, Trans. Amer. Geophys. Un., 62: 325.Google Scholar
  98. Turekian, K. K., and Cochran, J. K., Growth rate determination of a visicomyid clam from the Galapagos Spreading Center hydrothermal field using natural radionuclides, Earth Planet, Sci. Lett., in press.Google Scholar
  99. Van Andel, T. H., and Ballard, R. D., 1979, The Galapagos Rift at 86°W, 2, volcanism, structure and evolution of the rift valley, J. Geophys. Res., 84: 5390–5406.CrossRefGoogle Scholar
  100. Watts, A. B., 1982, Gravity anamolies over oceanic rifts,,a: “Continental and Oceanic Rifts,” G. Palmason, ed., Geodynamics Series 8, American Geophysical Union, 309 pp.Google Scholar
  101. Whitmarsh, R. B., 1975, Axial intrusion zone beneath the median valley of the Mid-Atlantic Ridge at 37°N detected by explosion seismology, Geophys. J. Roy. Astr. Soc. 42: 189–215.Google Scholar
  102. Williams, D., and Von Herzen, R. P., 1974, Heat loss from the earth: new estimate, Geology 2: 327–328.CrossRefGoogle Scholar
  103. Williams, D. L., Von Herzen, R. P., Sclater, J. G., and Anderson, R. H., 1974, The Galapagos Spreading Center: lithospheric cooling and hydrothermal circulation, Geoohys. J. Roy. Astr. Soc. 38: 587–608.CrossRefGoogle Scholar
  104. Woodside, J. M., 1972, The Mid-Atlantic Ridge near 45°N, the gravity field, Can. J. Earth Sci. 9: 942–959.CrossRefGoogle Scholar
  105. Young, P. D., and Cox, C. S., 1981, Electromagnetic active source sounding near the East Pacific Rise, Geophys. Res. Lett. 8: 1043–1046.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1983

Authors and Affiliations

  • Ken C. Macdonald
    • 1
  1. 1.Department of Geological Sciences, Marine Science InstituteUniversity of CaliforniaSanta BarbaraUSA

Personalised recommendations