Marine Geophysical Researches

, Volume 18, Issue 1, pp 53–84 | Cite as

Evolution of the East Pacific Rise at 16°–19° S since 5 Ma: Bisection of overlapping spreading centers by new, rapidly propagating ridge segments

  • Marie-Helene Cormier
  • Daniel S. Scheirer
  • Ken C. Macdonald
Article
Received:
Accepted:

Abstract

Nearly complete side-scan, bathymetry and magnetic coverage documents the evolution of the geometry of the East Pacific Rise (EPR) between 16° and 19° S since 5 Ma. Lineaments visible in SeaMARC II, H-MR1 and Sea Beam 2000 side-scan data correspond dominantly to normal fault scarps which have developed in the axial region perpendicular to the least compressive stress. Except near overlapping spreading centers (OSCs), the lineament orientations are taken to represent the perpendicular to the instantaneous Pacific-Nazca spreading direction. Their dominant orientation in the axial region is 012°, in good agreement with the prediction of the current model of relative plate motion (DeMets et al., 1994). However, the variations of the lineament azimuths with age show that there has been a small (3°–5°) clockwise change in the Nazca-Pacific relative motion since 5 Ma. There is also a distinct population of lineaments which strike counterclockwise to the ambient orientation. These discordant lineaments form somewhat coherent patterns on the seafloor and represent the past migration tracks of several left-stepping OSCs. Concurrent analysis of these discordant zones and the magnetic anomalies, reveals that up to 1 Ma, the EPR was offset by a few large, left-stepping OSCs. These OSCs were bisected into smaller OSCs by new spreading segments forming within their overlap basins. The smaller OSCs proceeded to migrate rapidly and were further bisected by newly spawned ridge segments until the present staircase of small, left-stepping OSCs was achieved. By transferring lithosphere from one plate to the other, these migration events account remarkably well for the variable spreading asymmetry in the area. Between 16° and 19° S, the present EPR is magmatically very “robust”, as evidenced by its inflated morphology, the profuse volcanic and hydrothermal activity observed from submerisbles and towed cameras, the geochemistry of axial basalts, and seismic and gravity data. Since 1 Ma, all the OSCs have migrated away from the shallowest, most robust section of the ridge between 17° and 17°30′ S, which was previously offset by a large OSC. We propose that the switch from a presumed starved magmatic regime typically associated with large OSCs to the presently robust magmatic regime occurred when the EPR overrode a melt anomaly during its westward migration relative to the asthenosphere. The resulting increase in melt supply at 17°–17°30′ S has fed the migration of axial discontinuities for this section of the southern EPR since 1 Ma.

Key words

East Pacific Rise discontinuity migration side-scan sonar data 
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References

  1. Alexander, R. T. and Macdonald, K. C., 1994, Distribution of Tectonic Deformation about the East Pacific Rise, 9°30′ N-Implications for the Formation of Abyssal Hills (abstract). Eos Trans. AGU, Spring Meeting Suppl. 75, 330.Google Scholar
  2. Atwater, T. and Severinghaus, J., 1989, Tectonic Maps of the Northeast Pacific, in Winterer, E. L., Hussong, D. M. and Decker, R. W. (eds.), The Geology of North America, N, The East Pacific Ocean and Hawaii, Geol. Soc. Am., 15–20.Google Scholar
  3. Auzende, J. M., Ballu, V., Batiza, R., Bideau, D., Cormier, M. H., Fouquet, Y., Geistdoerder, P., Lagabrielle, Y., Sinton, J. and Spadea, P., 1994, Observations of Present-Day Activity at Superfast Spreading: Volcanic, Hydrothermal and Tectonic Studies of the EPR 17°–19° S, Ridge Events 5, 1–2 and 20–21.Google Scholar
  4. Bach, W., Hegner, E., Erzinger, J. and Satir, M., 1994. Chemical and Isotopic Variations along the Superfast Spreading East Pacific Rise from 6° to 30° S, Contrib. Mineral. Petrol. 116, 365–380.Google Scholar
  5. Bäcker, H., Lange, J. and Marchig, V., 1985, Hydrothermal Activity and Sulfide Formation in Axial Valleys of the East Pacific Rise Crest between 18° and 22° S, Earth Planet. Sci. Lett. 72, 9–22.Google Scholar
  6. Bell, R. E. and Buck, W. R., 1992, Crustal Control of Ridge Segmentation Inferred from Observations of the Reykjanes Ridge, Nature 357, 583–586.Google Scholar
  7. Bicknell, J. D., Sempéré, J. C., Macdonald, K. C. and Fox, P. J., 1987, Tectonics of a Fast Spreading Center: A Deep-Tow and Sea Beam Survey on the East Pacific Rise at 19°30′ S, Mar. Geophys. Res. 9, 25–46.Google Scholar
  8. Bird, R. T. and Naar, D. F., 1994, Intratransform Origins of Mid-Ocean Ridge Microplates, Geology 22, 987–990.Google Scholar
  9. Cande, S. C. and Kent, D. V., 1992, A New Geomagnetic Polarity Time Scale for the Late Cretaceous and Cenozoic, J. Geophys. Res. 97 13,917–13,951.Google Scholar
  10. Cande, S. C., Raymond, C. A., Stock, J. and Haxby, W. F., 1995, Geophysics of the Pitman Fracture Zone and Pacific-Antarctic Plate Motions during the Cenozoic, Science 270, 947–951.Google Scholar
  11. Carbotte, S. and Macdonald, K. C., 1992, East Pacific Rise 8°–10°30′ N: Evolution of Ridge Segments and Discontinuities from SeaMARC II and Three-Dimensional Magnetic Studies, J. Geophys. Res. 97, 6959–6982.Google Scholar
  12. Carbotte, S. and Macdonald, K. C., 1994, Comparison of Seafloor Tectonic Fabric Created at Intermediate, Fast, and Superfast Spreading Ridges: Influence of Spreading Rate, Plate Motions and Ridge Segmentation on Fault Patterns, J. Geophys. Res. 99, 13,609–13,631.Google Scholar
  13. Chen, Y. J. and Morgan, W. J., 1990, Rift Valley/No Rift Valley Transition at Mid-Ocean Ridges, J. Geophys. Res. 95, 17571–17581.Google Scholar
  14. Choukroune, P., Francheteau, J. and Hékinian, R., 1984, Tectonics of the East Pacific Rise near 12°50′ N: A Submersible Study, Earth Planet. Sci. Lett. 68, 115–127.Google Scholar
  15. Cochran, J. R., 1986, Variations in Subsidence Rates Along Intermediate and Fast Spreading Mid-Ocean Ridges, Geophys. J. Roy. Astr. Soc. 87, 421–454.Google Scholar
  16. Cormier, M.-H. and Macdonald, K. C., 1994, East Pacific Rise 18°–19° S: Asymmetric Spreading and Ridge Reorientation by Ultra-Fast Migration of Axial Discontinuities, J. Geophys. Res. 99, 543–564.Google Scholar
  17. Cormier, M.-H., Macdonald, K. C. and Wilson, D. S., 1995, A Three-Dimensional Gravity Analysis of the East Pacific Rise, 18° to 21°30′ S, J. Geophys. Res. 100, 8063–8082.Google Scholar
  18. Davis, E. E. and Karsten, J. L., 1986, On the Cause of the Asymmetric Distribution of Seamounts about the Juan de Fuca Ridge: Ridge-Crest Migration Over a Heterogeneous Asthenosphere, Earth Planet. Sci. Lett. 79, 385–396.Google Scholar
  19. Davis, E. E. and Currie, R. G., 1993, Geophysical Observations of the Northern Juan de Fuca Ridge System: Lessons in Seafloor Spreading, Can. J. Earth Sci. 30, 278–300.Google Scholar
  20. DeMets, C., Gordon, R. G., Argus, D. F. and Stein, S., 1994, Effect of Recent Revisions to the Geomagnetic Reversal Time Scale on Estimates of Current Plate Motions, Geophys. Res. Lett. 21, 2191–2194.Google Scholar
  21. Detrick, R. S., Harding, A. H., 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
  22. Dziak, R. P., Fox, C. G. and Schreiner, A. E., 1995, The June–July 1993 Seismo-Acoustic Event at Coaxial Segment, Juan de Fuca Ridge: Evidence for a Lateral Dike Injection, Geophys. Res. Lett. 22, 135–138.Google Scholar
  23. 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
  24. Einarsson, P. and Brandsdottir, B., 1980, Seismological Evidence for Lateral Magma Intrusion during the July 1978 Deflation of the Krafla Volcano in NE Iceland, J. Geophys. 47, 160–165.Google Scholar
  25. Elvers, D., Srivastava, S. P., Potter, K., Morley, J. and Sdidel, D., 1973, Asymmetric Spreading Across the Juan de Fuca and Gorda Rises as Obtained from a Detailed Magnetic Survey, Earth Planet. Sci. Lett. 20, 211–219.Google Scholar
  26. Fernandez, L. S. and Hey, R. N., 1991, Late Tertiary Tectonic Evolution of the Seafloor Spreading System off the Coast of California between the Mendocino and Murray Fracture Zone, J. Geophys. Res. 96, 17955–17979.Google Scholar
  27. Fouquet, Y., Auzende, J.-M., Ballu, V., Batiza, R., Bideau, D., Cormier, M.-H., Geistdoerfer, P., Lagabrielle, Y., Sinton, J. and Spadea, P., 1994, Variabilité des manifestations hydrothermales actuelles le long d'une dorsale ultra rapide. Dorsale Est Pacifique entre 17° et 19° S (campagne NAUDUR), Comptes Rendus Acad. Sci. 319, series II, 1399–1406.Google Scholar
  28. Gente, P., Auzende, J.-M., Renard, V., Fouquet, Y. and Bideau, D., 1986, Detailed Geological Mapping by Submersible of the East Pacific Rise Axial Graben Near 13° N, Earth Planet. Sci. Lett. 78, 224–236.Google Scholar
  29. Gente, P., Pockalny, R. A., Durand, C., Deplus, C., Maia, M., Ceuleneer, G., Mével, C., Cannat, M. and Laverne, C., 1995, Characteristics and Evolution of the Segmentation of the Mid-Atlantic Ridge Between 20° N and 24° N during the Last 10 Million Years, Earth Planet. Sci. Lett. 129, 55–71.Google Scholar
  30. Goff, 1991, A Global and Regional Stochastic Analysis of Near-Ridge Abyssal Hill Morphology, J. Geophys. Res. 96, 21713–21737.Google Scholar
  31. Gripp, A. E. and Gordon, R. G., 1990, Current Plate Velocities Relative to the Hot Spots Incorporating the NUVEL-1 Global Plate Motion Model, Geophys. Res. Lett. 17, 1109–1112.Google Scholar
  32. Handschumacher, D. W., PilgerJr., R. H., Foreman, J. A. and Campbell, J. F., 1981, Structure and Evolution of the Easter Plate, in Kulm, L. D. et al. (eds), Nazca Plate: Crustal Formation and Andean Convergence, Geol. Soc. Am. Memoir 154, 63–76.Google Scholar
  33. Harbert, W. and Cox, A., 1989, Late Neogene Motion of the Pacific Plate, J. Geophys. Res. 94, 3052–3064.Google Scholar
  34. Haxby, W. F. and Weissel, J. K., 1986, Evidence for Small Scale Mantle Convection from SeaSat Altimeter Data, J. Geophys. Res. 93, 6419–6429.Google Scholar
  35. Hayes, D. E., 1976, Nature and Implications of Asymmetric Seafloor Spreading-“Different Rates for Different Plates”. Geol. Soc. Am. Bull. 87, 994–1002.Google Scholar
  36. Haymon, R. M., Fornari, D. J., Edwards, M. H., Carbotte, S., Wright, D. and Macdonald, K. C., 1991, Hydrothermal Vent Distribution Along the East Pacific Rise Crest (9°09′–54′ N) and Its Relationship to Magmatic and Tectonic Processes on Fast Spreading Mid-Ocean Ridges, Earth Planet. Sci. Lett. 104, 513–534.Google Scholar
  37. Hékinian, R., Auzende, J. M., Francheteau, J., Gente, P., Ryan, W. B. F. and Kappel, E. S., 1985, Offset Spreading Centers Near 12°53′ N on the East Pacific Rise: Submersible Observations and Composition of the Volcanics, Mar. Geophys. Res. 7, 359–377.Google Scholar
  38. Hey, R., Johnson, G. L. and Lowrie, A., 1977, Recent Plate Motions in the Galapagos Area, Geol. Soc. Am. Bull. 88, 1385–1403.Google Scholar
  39. Hey, R., Duennebier, F. K. and Morgan, W. J., 1980, Propagating Rifts on Mid-Ocean Ridges, J. Geophys. Res. 85, 3647–3658.Google Scholar
  40. Hey, R. N., Kleinrock, M. C., Miller, S. P., Atwater, T. M. and Searle, R. C., 1986, Sea Beam/Deep Tow Investigation of an Active Oceanic Propagating Rift System, Galapagos 95.5° W, J. Geophys. Res. 91, 3369–3393.Google Scholar
  41. Hilgen, F. J., 1991, Extension of the Astronomically Calibrated (Polarity) Time Scale to the Miocene/Pliocene Boundary, Earth Planet. Sci. Lett. 107, 349–368.Google Scholar
  42. Holler, G., Marchig, V. and the Shipboard Scientific Party, 1990, Hydrothermal Activity on the East Pacific Rise: Stages of Development, Geol. Jarb. B75, 3–22.Google Scholar
  43. Jha, K., Parmentier, E. M. and Phipps Morgan, J., 1993, Episodic Three-Dimensional Mantle Upwelling and Crustal Production Beneath a Spreading Center (abstract), Eos Trans. AGU 74, 304.Google Scholar
  44. Klein, F. W., Koyanagi, R. Y., Nakata, J. S. and tanigawa, W. R., 1987, The Seismicity of Kilauea's Magma System, U.S. Geol. Surv. Prof. Paper 1350, 1019–1186.Google Scholar
  45. Kleinrock, M. C., Searle, R. C. and Hey, R. N., 1989, Tectonics of the Failing Spreading System Associated with the 95.5° W Galapagos Propagator, J. Geophys. Res. 94, 13,839–13,857.Google Scholar
  46. Kleinrock, M. C., Hey, R. N. and ThebergeJr., A. E., 1992, Practical Geological Comparison of Some Seafloor Survey Instruments, Geophys. Res. Lett. 19, 1407–1410.Google Scholar
  47. Kuykendall, M. G., Kruse, S. E. and McNutt, M. K., 1994, The Effects of Changes in Plate Motions on the Shape of the Marquesas Fracture Zone, Geophys. Res. Lett. 21, 2845–2848.Google Scholar
  48. Lonsdale, P., 1977, Structural Geomorphology of a Fast-Spreading Rise Crest: The East Pacific Rise near 3°25′ S, Mar. Geophys. Res. 3, 251–293.Google Scholar
  49. 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
  50. Lonsdale, P., 1985, Nontransform Offsets of the Pacific-Cocos Plate Boundary and Their Traces on the Rise Flank, Geol. Soc. Am. Bull. 96, 313–327.Google Scholar
  51. Lonsdale, P., 1989a, The Rise Flank Trails Left by Migrating Offsets of the Equatorial East Pacific Rise Axis, J. Geophys. Res. 94, 713–743.Google Scholar
  52. Lonsdale, P., 1989b, Segmentation of the Pacific-Nazca Spreading Center, 1° N – 20° S, J. Geophys. Res. 94, 12,197–12,226.Google Scholar
  53. Lonsdale, P., 1994, Geomorphology and Structural Segmentation of the Crest of the Southern (Pacific-Antarctic) East Pacific Rise, J. Geophys. Res. 99, 4683–4702.Google Scholar
  54. Macario, A., 1995, Crustal Accretion at Intermediate Spreading Rates: Pacific-Antarctic Ridge at 65° S, Ph.D. Thesis, Columbia University, NY, 209 pages.Google Scholar
  55. Macdonald, K. C., 1977, Near-Bottom Magnetic Anomalies, Asymmetric Spreading, Oblique Spreading, and Tectonics of the Mid-Atlantic Ridge Near Lat. 37° N, Geol. Soc. Am. Bull. 88, 541–555.Google Scholar
  56. 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.Google Scholar
  57. Macdonald, K. C. and Fox, P. J., 1983, Overlapping Spreading Centers: New Accretion Geometry on the East Pacific Rise, Nature 303, 549–550.Google Scholar
  58. Macdonald, K. C., Sempéré, 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 Centers, J. Geophys. Res. 89, 6049–6069.Google Scholar
  59. Macdonald, K. C. and Luyendyk, B. P., 1985, Investigation of Faulting and Abyssal Hill Formation on the Flanks of the East Pacific Rise (21° N) Using Alvin, Mar. Geophys. Res. 7, 515–535.Google Scholar
  60. Macdonald, K. C., Sempéré, J. C., Fox, P. J. and Tyce, R., 1987, Tectonic Evolution of Ridge-Axis Discontinuities by the Meeting, Linking, or Self-Decapitation of Neighboring Ridge Segments, Geology 15, 993–997.Google Scholar
  61. Macdonald, K. C., Fox, P. J., Perram, L. J., Eisen, M. F., Haymon, R. M., Miller, S. P., Carbotte, S. M., Cormier, M.-H. and Shor, A. N., 1988a, A New View of the Mid-Ocean Ridge from the Behavior of Ridge Axis Discontinuities, Nature, 335, 217–225.Google Scholar
  62. Macdonald, K. C., Haymon, R. M., Miller, S. P. and Sempéré, J. C., 1988b, Deep-Tow and Sea Beam Studies of Dueling Propagating Ridges on the East Pacific Rise near 20°40′ S, J. Geophys. Res. 93, 2875–2898.Google Scholar
  63. Macdonald, K. C. and Fox, P. J., 1988, The Axial Summit Graben and Cross-Sectional Shape of the East Pacific Rise as Indicators of Axial Magma Chambers and Recent Volcanic Eruptions, Earth Planet. Sci. Lett. 88, 119–131.Google Scholar
  64. Macdonald, K. C., Scheirer, D. S. and Carbotte, S. M., 1991, Mid-Ocean Ridges: Discontinuities, Segments and Giant Cracks, Science 253, 986–994.Google Scholar
  65. Macdonald, K. C., Fox, P. J., Miller, S. P., Carbotte, S. M., Edwards, M. H., Eisen, M., Fornari, D. J., Perram, L. J., Pockalny, R., Scheirer, D. S., Tighe, S., Weiland, C. and Wilson, D. S., 1992, The East Pacific Rise and Its Flanks 8°–18° N: History of Segmentation, Propagation and Spreading Direction Based on Sea-MARC II and Sea Beam Studies, Mar. Geophys. Res. 14, 299–344.Google Scholar
  66. Macdonald, K. C., Fox, P. J., Alexander, R. T., Pockalny, R. and Gente, P., 1996, Volcanic Growth Faults and the Origin of Abyssal Hills, Nature (March).Google Scholar
  67. Madsen, J. A., Fornari, D. J., Edwards, M. H., Gallo, D. G. and Perfit, M. R., 1992, Kinematic Framework of the Cocos-Pacific Plate Boundary from 13° N to the Orozco Transform Fault: Results from an Extensive Magnetic and SeaMARC II Survey, J. Geophys. Res. 97, 7011–7024.Google Scholar
  68. Mahoney, J. J., Sinton, J. M., 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
  69. 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
  70. Molnar, P., Atwater, T., Mammerickx, J. and Smith, S. M., 1975, Magnetic Anomalies, Bathymetry and the Tectonic Evolution of the South Pacific Since the Late Cretaceous, Geophys. J. R. Astr. Soc. 40, 383–420.Google Scholar
  71. Morton, J. L. and Ballard, R. D., 1986, East Pacific Rise at Latitude 19° S: Evidence for a Recent Ridge Jump, Geology 14, 111–114.Google Scholar
  72. Mutter, J. C., Carbotte, S. M., Su, W., Xu, L., Buhl, P., Detrick, R. S., Kent, G. M., Orcutt, J. A. and Harding, A. J., 1995, Seismic Images of Active Magma Systems Beneath the East Pacific Rise Between 17°5′ and 17°35′ S, Science 268, 391–395.Google Scholar
  73. Naar, D. F. and Hey, R. N., 1989, Recent Pacific-Easter-Nazca Plate Motions, in Sinton, J. M. (ed.), Evolution of Mid-Ocean Ridges, Geophysical Monograph 57, 9–30.Google Scholar
  74. Naar, D. F. and Hey, R. N., 1991, Tectonic Evolution of the Easter Microplate, J. Geophys. Res., 96, 7961–7993.Google Scholar
  75. Pariso, J. E., Sempéré, J. C. and Rommevaux, C., 1995, Temporal and Spatial Variations in Crustal Accretion Along the Mid-Atlantic Ridge (29°–31°30′ N) over the last 10 m.y.: Implications from a Three-Dimensional Gravity Study, J. Geophys. Res 100, 17781–17794.Google Scholar
  76. Parson, L. M., Pearce, J. A., Murton, B. J., Hodkinson, R. A. and RRS Charles Darwin Scientific Party, 1990, Role of Ridge Jumps and Ridge Propagation in the Tectonic Evolution of the Lau Back-Arc Basin, Southwest Pacific, Geology, 18, 470–473.Google Scholar
  77. Perram, L. J. and Macdonald, K. C., 1990, A One-Million-Year History of the 11°45′ N East Pacific Rise Discontinuity, J. Geophys. Res. 95, 21363–21381.Google Scholar
  78. Perram, L. J., Cormier, M.-H. and Macdonald, K. C., 1993, Magnetic and Tectonic Studies of the Dueling Propagating Spreading Centers at 20°40′ S on the East Pacific Rise: Evidence for Crustal Rotations, J. Geophys. Res. 98, 13835–13850.Google Scholar
  79. 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.Google Scholar
  80. Phipps Morgan, J., 1991, Mid-ocean Ridge Dynamics: Observations and Theory, Reviews Geophys., Supplement, 807–822.Google Scholar
  81. Phipps Morgan, J. and Sandwell, D. T., 1994, Systematics of Ridge Propagation South of 30° S, Earth Planet. Sci. Lett. 121, 245–258.Google Scholar
  82. Phipps Morgan, J., Morgan, W. J., Zhang, Y.-S. and Smith, W. H. F., 1995, Observational Hints for a Plume-Fed, Sub-Oceanic Asthenosphere and Its Role in Mantle Convection, J. Geophys. Res. 100, 12753–12767.Google Scholar
  83. Pollard, D. D. and Aydin, A., 1984, Propagation and Linkage of Oceanic Ridge Segments, J. Geophys. Res. 89, 10017–10028.Google Scholar
  84. Pollitz, F. F., 1986, Pliocene Change in Pacific-Plate Motion, Nature 320, 738–741.Google Scholar
  85. Press, W. H., Flannery, B. P., Teukolsky, S. A. and Vettering, W. T., 1986, Numerical Recipes: The Art of Scientific Programming, Cambridge University Press.Google Scholar
  86. Rea, D. K., 1981, Tectonics of the Nazca-Pacific Divergent Plate Boundary, in Kulm, L. D. et al. (eds.), Nazca Plate: Crustal Formation and Andean Convergence, Geol. Soc. Am. Memoir 154, 27–62.Google Scholar
  87. Renard, V., Hékinian, 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′ to 21°30′ S), Earth Planet. Sci. Lett. 75, 339–353.Google Scholar
  88. Scheirer, D. S. and Macdonald, K. C., 1993, The 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
  89. Scheirer, D. S., Macdonald, K. C. and Forsyth, D. W., 1993, Widespread Volcanic and Tectonic Activity on the Southern East Pacific Rise and Its Flanks, RIDGE Events 4, 1–2 and 8–10.Google Scholar
  90. Scheirer, D. S., Macdonald, K. C., Forsyth, D. W., Miller, S. P., Wright, D. J., Cormier, M.-H. and Weiland, C. M., 1996, A Map Series of the Southern East Pacific Rise and Its Flanks, 15° S to 19° S, Mar. Geophys. Res., 18, 1–12 (this issue).Google Scholar
  91. Schilling, J. G., 1991, Fluxes and Excess Temperatures of Mantle Plumes Inferred from Their Interaction with Migrating Mid-Ocean Ridges, Nature 352, 397–403.Google Scholar
  92. Searle, R. C., 1983, Multiple, Closely Spaced Transform Faults in Fast-Slipping Fracture Zones, Geology 11, 607–610.Google Scholar
  93. Searle, R. C., Rusby, R. I., Engeln, J., Hey, R. N., Zukin, J., Hunter, P. M., LeBas, T. P., Hoffman, H. J. and Livermore, R., 1989, Comprehensive Sonar Imaging of the Easter Microplate, Nature 341, 701–705.Google Scholar
  94. Sempéré, J. C. and Macdonald, K. C., 1986, Overlapping Spreading Centers: Implications from Crack Growth Simulation by the Discontinuity Method, Tectonics 5, 151–163.Google Scholar
  95. Shaw, P. R. and Lin, J., 1993, Causes and Consequences of Variations in Faulting Style at the Mid-Atlantic Ridge, J. Geophys. Res. 98, 21839–21851.Google Scholar
  96. Shen, Y., Forsyth, D. W., Scheirer, D. S. and Macdonald, K. C., 1993, Two Forms of Volcanism: Implications for the Volume of Off-Axis Crustal Production on the West Flank of the East Pacific Rise, J. Geophys. Res. 98, 17,875–17,889.Google Scholar
  97. Sinha, M. C., 1995, Segmentation and Rift Propagation at the Valu Fa Ridge, Lau Basin: Evidence from Gravity Data, J. Geophys. Res. 100, 15025–15043.Google Scholar
  98. Sinton, J. M., Smaglik, S. M., Mahoney, J. J. and Macdonald, K. C., 1991, Magmatic Processes at Superfast Mid-Ocean Ridges: Glass Compositional Variations along the East-Pacific Rise 13°–23° S, J. Geophys. Res. 96, 6133–6155.Google Scholar
  99. Stein, S., Mellosh, H. J. and Minster, J. B., 1977, Ridge Migration and Asymmetric Seafloor Spreading, Earth Planet. Sci. Lett. 36, 51–62.Google Scholar
  100. Tawalni, M., Windish, C. C. and LangsethJr., M. G., 1971, Reykjanes Ridge Crest: A Detailed Geophysical Study, J. Geophys. Res. 76, 473–517.Google Scholar
  101. Tighe, S. A., Detrick, R. S., Fox, P. J., Langmuir, C. H., Mutter, J. C., Ryan, W. B. and Tyce, R. C., 1988, East Pacific Rise Data Synthesis, Final Report, vol. 1, Joint Ocean. Inst. Inc., Washington, D.C.Google Scholar
  102. 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
  103. Urabe, T., Baker, E. T. and 28 other researchers, 1995, The Effect of Magmatic Activity on Hydrothermal Venting Along the Superfast-Spreading East Pacific Rise, Science 269, 1092–1095.Google Scholar
  104. Wang, X. and Cochran, J. R., 1993, Gravity Anomalies, Isostasy, and Mantle Flow at the East Pacific Rise Crest, J. Geophys. Res. 98, 19,505–19,531.Google Scholar
  105. Wang, X., Cochran, J. R. and Barth, G. A., 1995, Gravity Anomalies, Crustal Thicknesses and the Pattern of Mantle Flow at the Fast Spreading East Pacific Rise, 9°–10° N: Evidence for Three-Dimensional Upwelling, J. Geophys. Res., in press.Google Scholar
  106. Weissel, J. K. and Hayes, D. E., 1977, The Australian-Antarctic Discordance: New Results and Implications, J. Geophys. Res. 79, 2579–2587.Google Scholar
  107. Wessel, P. and Smith, W. H. F., 1993, The GMT-SYSTEM, v. 2.1.4, Technical Reference and Cookbook, SOEST/SIO.Google Scholar
  108. Wilson, D. S., Hey, R. N. and Nishimura, C., 1984, Propagation as a Mechanism of Reorientation of the Juan de Fuca Plate, J. Geophys. Res. 91, 9215–9225.Google Scholar
  109. Wilson, D. S., 1988, Tectonic History of the Juan de Fuca Ridge over the Last 40 Million Years, J. Geophys. Res. 93, 11863–11876.Google Scholar
  110. Wilson, D. S., 1990, Kinematics of Overlapping Rift Propagation with Cyclic Rift Failure, Earth Planet. Sci. Lett. 96, 384–392.Google Scholar
  111. 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
  112. Wilson, D. S., 1993a, Confidence Intervals for Motion and Deformation of the Juan de Fuca Plate, J. Geophys. Res. 98, 16,053–16,072.Google Scholar
  113. Wilson, D. S., 1993b, Confirmation of the Astronomical Calibration of the Magnetic Polarity Timescale from Seafloor Spreading Rates, Nature 364, 788–790.Google Scholar

Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • Marie-Helene Cormier
    • 1
  • Daniel S. Scheirer
    • 1
  • Ken C. Macdonald
    • 1
  1. 1.Department of Geological SciencesUniversity of CaliforniaSanta BarbaraUSA

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