Advertisement

Marine Geophysical Researches

, Volume 21, Issue 1–2, pp 23–41 | Cite as

Volcanic Morphology of the East Pacific Rise Crest 9°49′–52′: Implications for volcanic emplacement processes at fast-spreading mid-ocean ridges

  • Gregory J. Kurras
  • Daniel J. Fornari
  • Margo H. Edwards
  • Michael R. Perfit
  • Matthew C. Smith
Article

Abstract

Deep sea photographs were collected for several camera-tow transects along and across the axis at the East Pacific Rise crest between 9°49′ and 9°52′ N, covering terrain out to 2 km from the ridge axis. The objective of the surveys was to utilize fine-scale morphology and imagery of seafloor volcanic terrain to aid in interpreting eruptive history and lava emplacement processes along this fast-spreading mid-ocean ridge. The area surveyed corresponds to the region over which seismic layer 2A, believed to correspond to the extrusive oceanic layer, attains full thickness (Christeson et al., 1994a, b, 1996; Hooft et al., 1996; Carbotte et al., 1997). The photographic data are used to identify the different eruptive styles occurring along the ridge crest, map the distribution of the different morphologies, constrain the relative proportions of the three main morphologies and discuss the implications of these results. Morphologic distributions of lava for the area investigated are 66% lobate lava, 20% sheet lava, 10% pillow lava, and 4% transitional morphologies between the other three main types. There are variations in inferred relative lava ages among the different morphological types that do not conform to a simple increase in age versus distance relationship from the spreading axis, suggesting a model in which off-axis transport and volcanism contribute to the accumulation of the extrusive layer. Analysis of the data suggests this ridge crest has experienced three distinctly different types of volcanic emplacement processes: (1) axial summit eruptions within a ∼1 km wide zone centered on the axial summit collapse trough (ASCT); (2) off-axis transport of lava erupted at or near the ASCT through channelized surface flows; and (3) off-axis eruptions and local constructional volcanism at distances of ∼0.5-1.5 km from the axis. Major element analyses of basaltic glasses from lavas collected by Alvin, rock corer and dredging in this area indicate that the most recent magmatic event associated with the present ASCT erupted relatively homogeneous and mafic (>8.25 weight percent wt.% MgO) basalts compared to older, off-axis lavas which tend to be more chemically evolved (Perfit and Chadwick, 1998; Perfit and Fornari, unpublished data). The more primitive lavas have a more extensive distribution within and east of the ASCT. More evolved basalts (MgO <8.0wt.%) are concentrated in a broad area a few kilometers east of the axis, and in an oval-shaped area south of 9°50′ N, west of the ASCT. Transitional and enriched (T- and E-) mid-ocean ridge basalts exist in relatively small areas (<1 km2) on the crestal plateau and correlate with scarps or fissures where pillow lavas were erupted. Mafic lavas in this area are primarily related to the youngest magmatic events. Geochemical analysis of samples collected at distances >∼500 m from the ASCT suggests that regions of off-axis volcanism may be sourced from older and cooler sections of the axial magma lens. Analysis of these data suggests that this portion of the EPR has not experienced large scale volcanic overprinting in the past ∼30 ka. The predominance of lobate flows (66%) throughout much of the crestal region, and subtle variations in sediment cover and apparent age between flows, suggest that eruptive volumes and effusion rates of individual eruptions have been similar over much of the last 30 ka and that most of the eruptions have been small, probably similar in volume to the 1991 EPR flow which had an estimated volume of ∼1×106 m3 (Gregg et al., 1996).

Keywords

Effusion Rate Pillow Lava Magmatic Event Ridge Crest Mafic Lava 
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. Ballard, R.D. and Van Andel, T.H., 1977, Morphology and tectonics of the inner rift valley at lat 36°50′ N on the mid-Atlantic ridge, Geol. Soc. America Bull. 88: 507–530.Google Scholar
  2. Ballard R.D., Van Andel, T.H. and Holcomb, R.T., 1982a, The Galapagos Rift at 86° W, 5. Variations in volcanism, structure, and hydrothermal activity along a 30-kilometer segment of the rift valley, J. Geophys. Res. 87: 1149–1161.Google Scholar
  3. Ballard, R.D. and Francheteau, J., 1982b, The relationship between active sulfide deposition and the axial processes of the mid-ocean ridge, Mar. Technol. Soc. J. 16: 8–20.Google Scholar
  4. Ballard, R.D., Hekinian, R. and Francheteau, J., 1984, Geological setting of hydrothermal activity at 12°50′ N on the East Pacific Rise: A submersible study, Earth Planet. Sci. Lett. 69: 176–186.Google Scholar
  5. Bonatti, E. and Harrison, C.G., 1988, Eruption styles of basalt in oceanic spreading ridges and seamounts: effect of magma temperature and viscosity, J. Geophys. Res. 93: B4, 2967–2980.Google Scholar
  6. Carbotte, S.M. and Macdonald, K.C., 1992, East Pacific Rise 8° N–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
  7. Carbotte, S.M. and Macdonald, K.C., 1994, The axial topographic high at intermediate and fast spreading ridges, Earth Planet. Sci. Lett. 128: 85–97.Google Scholar
  8. Carbotte, S.M., Mutter, J.C. and Xu, L., 1997, Contribution of volcanism and tectonism to axial and flank morphology of the southern EPR, 17°10′–17°40′ S, from a study of Layer 2A geometry, J. Geophys. Res. 102: 10,165–10,184.Google Scholar
  9. Chadwick, W.W., Gregg, T.K.P. and Embley, R.W., 1999, Submarine lineated sheet flows: a unique lava morphology formed on subsiding lava ponds, Bull. Volcanol. 61: 194–206.Google Scholar
  10. Christeson, G.L., Purdy, G.M. and Fryer, G.L., 1992, Structure of young oceanic crust at the East Pacific Rise near 9°30′ N, Geophys. Res. Lett. 19: 1045–1048.Google Scholar
  11. Christeson, G.L., Purdy, G.M. and Fryer, G.J., 1994a, Seismic constraints on shallow crustal emplacement processes at the fast spreading East Pacific Rise,J. Geophys. Res. 99, 17,957–17,974.Google Scholar
  12. Christeson, G.L., Wilcock, W.S.D. and Purdy, G.M., 1994b, The shallow attenuation structure of the fast spreading East Pacific Rise near 9°30′ N,Geophys. Res. Lett. 21: 321–324.Google Scholar
  13. Christeson, G.L., Kent, G.M., Purdy, G.M. and Detrick, R.S., 1996, Extrusive thickness variability at the East Pacific Rise, 9°–10° N: Constraints from seismic techniques, J. Geophys. Res. 101: 2859–2873.Google Scholar
  14. Cochran, J.R., Fornari, D.J., Coakley, B.J. and Herr, R., 1996, Nearbottom underway gravity study of the shallow structure of the axis of the East Pacific Rise, 9°31′ N and 9°50′ N, EOS Trans. AGU 77(46): F698–F699.Google Scholar
  15. Cochran, J.R., Fornari, D.J., Coakley, B.J., Herr, R. and Tivey, M.A., 1999, Continuous near-bottom gravity measurements made with a BGM-3 gravimeter in DSV Alvin on the East Pacific Rise crest 9°30′ and 9°50′ N, J Geophys. Res. 104(5): 10841–10861.Google Scholar
  16. Dragoni, M., 1993, Modeling the rheology and cooling of lava flows, in Kilburn C.R.J. and Luongo G. (eds), Active Lavas, London, UCL Press Limited, pp. 235–258.Google Scholar
  17. Edwards, M.H., Fornari, D.J., Malinverto, 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
  18. Embley, R.W., Murphy, K.M., and Fox, C.G., 1990, High-resolution studies of the summit of axial volcano, J. Geophys. Res. 95, (B8): 12785–12812.Google Scholar
  19. Fornari, D.J. and Spencer, W.D., 1998, Woods Hole Oceanographic Institution Towed Camera Sled, Technical and Operations Manual, WHOI Tech. Report, pp. 10.Google Scholar
  20. Fornari, D.J., Kurras, G.J., Edwards, M.H., Spencer, W., and Hersey, W., 1998a, Mapping volcanic morphology on the crest of the East Pacific Rise 9°49′–52′ N using theWHOI towed camera system: a versatile new digital camera sled for seafloor mapping, BRIDGE Newsletter 14: 4–12.Google Scholar
  21. Fornari, D.J., Haymon, R.M., Perfit, M.R., Gregg, T.K.P., and Edwards, M. H., 1998b, Axial summit trough of the East Pacific Rise 9°–10° N: Geological Characteristics and Evolution of the Axial Zone on Fast Spreading Mid-Ocean Ridges, J. Geophys. Res. 103, (B5): 9827–9855.Google Scholar
  22. Fornari, D.J. and Embley, R.W., 1995, Tectonic and volcanic controls on hydrothermal processes at the mid-ocean ridge: An overview based on near-bottom and submersible studies, seafloor hydrothermal systems: physical, chemical, biological, and geological interactions, in Humphris S. et al. (eds), Geophys. Monogr. Ser. 91, AGU, Washington, D.C., pp. 1–46.Google Scholar
  23. Goldstein, S.J., Perfit, M.R., Batiza, R., Fornari, D.J., and Murrell, M.T., 1994, Off-axis volcanism at the East Pacific Rise detected by uranium-series dating of basalts, Nature 367: 157–159.Google Scholar
  24. Griffiths, R.W. and Fink, J.H., 1992, Solidification and morphology of submarine lavas: A dependence on extrusion rate, J. Geophys. Res. 97: 19729–19737.Google Scholar
  25. Gregg, T.K.P. and Fink, J.H., 1995, Quantification of submarine lava-flow morphology through analog experiments, Geology 23: 73–76.Google Scholar
  26. Gregg, T.K.P., Fornari, D.J., Perfit, M.R., Haymon, M.R., and Fink, J.H., 1996, Rapid emplacement of a mid-ocean ridge lava flow on the East Pacific Rise at 9°46′–51′ N, Earth Planet. Sci. Lett. 144: E2.Google Scholar
  27. Gregg, T.K.P. and Keszthelyi, L.P., The emplacement of Pahoehoe toes: Field observations and comparison to laboratory simulations, Bull. Volcanol. (submitted). Google Scholar
  28. Harding, A.J., Kent, G.M., and Orcutt, J.A., 1993, A multichannel seismic investigation of the upper crustal structure at 9° N on the East Pacific Rise: Implications for crustal accretion, J. Geophys. Res. 98: 13,925–13,944.Google Scholar
  29. Haymon, R., Fornari, D., Edwards, M. et al., 1991, Hydrothermal vent distribution along the East Pacific Rise Crest (9°09′–54′ N) and its relationship to magmatic and tectonic processes on fastspreading Mid-Ocean Ridge, Earth Planet. Sci. Lett. 104: 513–534.Google Scholar
  30. Haymon, R., Fornari, D., Von Damm, K. et al., 1993, Volcanic eruption of the mid-ocean ridge along the East Pacific Rise at 9°45–52′ N: Direct submersible observation of seafloor phenomena associated with an eruption event in April, 1991,Earth Planet. Sci. Lett. 119: 85–101.Google Scholar
  31. Head, J.W. III, Wilson, L., and Smith, D.K., 1996, Mid-ocean ridge eruptive vent morphology and substructure: Evidence for dike widths, eruption rates, and evolution of eruptions and axial volcanic ridges, J. Geophys. Res. 101(12): 28265–28280.Google Scholar
  32. Hooft, E.E.E., Schouten, H., and Detrick, R.S., 1996, Constraining crustal emplacement processes from the variation of seismic layer 2A thickness at the East Pacific Rise, Earth Planet. Sci. Lett. 142: 289–309.Google Scholar
  33. Hon, K., Kauahikaua, J., Denlinger, R., and Mackay, K., 1994, Emplacement and inflation of pahoehoe sheet flows: Observations and measurements of active lava flows on Kilauea Volcano, Hawai'i, Geological Soc. Of America Bull. 106: 351–370.Google Scholar
  34. Kurras, G.J., Edwards, M.H., and Fornari, D.J., 1998, Highresolution bathymetry of the East Pacific Rise axial summit trough 9°49′–51′ N: A compilation of Alvin scanning sonar and altimetry data from 1991–1995, Geophys. Res. Lett. 25, (8): 1209–1212.Google Scholar
  35. Langmuir, C.H., Bender, J.F., and Batiza, R., 1986, Petrologic and tectonic segmentation of the East Pacific Rise, 5°30′–14°30′ N, Nature 322: 422–429.Google Scholar
  36. Lonsdale, P.F., 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
  37. 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 centers: J. Geophys. Res. 89: 6049–6069.Google Scholar
  38. Macdonald, K.C., 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
  39. Macdonald, K.C., Haymon, R.M., Shor, A., 1989, A 220 km2 recently erupted lava field on the East Pacific Rise near lat 8° S, Geology 17: 212–216.Google Scholar
  40. Macdonald, K.C., Fox, P.J., Alexander, R.T., Pockalny, R., and Gente, P., 1996, Volcanic growth faults and the origin of abyssal hills on the flanks of the East Pacific Rise, Nature 380: 125–129.Google Scholar
  41. McBirney, A.R., and Murase, T., 1984, Rheological properties of magmas: Ann. Rev. Earth Planet. Sci. 12: 337–357.Google Scholar
  42. Perfit, M.R., Fornari, D.J., Smith, M.C., Bender, J.F., Langmuir, C.H., and Haymon, R.M., 1994, Small-scale spatial and temporal variations in mid-ocean ridge crest magmatic processes, Geology 22: 375–379.Google Scholar
  43. Perfit, M.R., Smith, M.C., Sapp, K., Fornari, D.J., Gregg, T., Edwards, M.H., Ridley, W.I., and Bender, J.F., 1995, Geochemistry and morphology of the crestal plateau of the East Pacific Rise 9°50′ N, EOS Trans. AGU 76(46): F694.Google Scholar
  44. Perfit, M., Fornari, D., Ridley, W.I., Kirk, P.D., Casey, J., and Kastens, K.A., 1996, Recent volcanism in the Siqueiros transform fault: picirtic basalts and implications for MORB magma genesis, Earth Planet. Sci. Lett. 141: 91–108.Google Scholar
  45. Perfit, M.R. and Chadwick, W.C., 1998, Magmatism at mid-ocean ridges: Constraints from volcanological and geochemical investigations, in: Faulting and magmatism at mid-ocean ridges, W.R. Buck, et al. (eds.), Am. Geophys. U. Geophys. Monograph 106: 59–116.Google Scholar
  46. Reynolds, J.R. and Langmuir, C.H., 1998, Identification and implications of off-axis lava flows around the East Pacific Rise, Earth Planet. Sci. Lett. (in press).Google Scholar
  47. Rowland, S.K. and Walker, G.P., 1990, Pahoehoe and aa in Hawaii: Volumetric flow rate controls the lava structure, Bull. Volcanol. 52: 615–628.Google Scholar
  48. Rubin, K.H., Macdougall, J.D., and Perfit, M.R.,1994, 210Po-210Pb dating of recent volcanic eruptions on the seafloor, Nature 368: 841–844.Google Scholar
  49. Scheirer, D.S. and Macdonald, K.C., 1993, Variation in crosssectional 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
  50. Schouten, H., Tivey, M.A., Fornari, D.J., and Cochran, J.R., 1999, Central anomaly magnetization high: constraints on the volcanic construction and architecture of seismic layer 2A at a fast-spreading mid-ocean ridge, the EPR at 9°30–50′ N, Earth Planet. Sci. Lett. 169: 37–50.Google Scholar
  51. Sims K., Fornari, D., Goldstein, S., Perfit, M.R., Hart, S.R., Smith, M.C., and Murrel, M.T., 1997, U-series analyses of young lavas from 9–10° N East Pacific Rise: constraints on magma transport and storage times beneath the ridge axis, Trans. Amer. Geophys. Union, EOS 78: 792.Google Scholar
  52. Sinton, J.M. and Detrick, R.S., 1992, Mid-ocean ridge magma chambers, J. Geophys. Res. 97: 197–216.Google Scholar
  53. Smith, M.C., Perfit, M.R., Embley, R., and Chadwick, W.W., 1997, Interpretation of magmatic activity and crustal accretion along the CoAxial and Axial seamount north rift zone: using combined acoustic and geochemical data to map the seafloor at the scale of individual flows, Trans. Am. Geophys. Union, EOS 78: F676.Google Scholar
  54. Thompson, G., Bryan, W.B., Ballard, R., Hamuro, K., and Melson, W.G., 1985, Axial processes along a segment of the East Pacific Rise, 10°–12° N, Nature 318(6045): 429–433.Google Scholar
  55. Weaver, J.S. and Langmuir, C.H., 1990, Calculations of phase equilibrium in mineral-melt systems, Comp. Geosci. 16: 1–19.Google Scholar

Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • Gregory J. Kurras
    • 1
  • Daniel J. Fornari
    • 2
  • Margo H. Edwards
    • 3
  • Michael R. Perfit
    • 4
  • Matthew C. Smith
    • 1
  1. 1.Department of Marine Geology and Geophysics, School of Ocean Earth Science and TechnologyUniversity of Hawai`iHonoluluUSA (Ph
  2. 2.Department of Geology and GeophysicsWoods Hole Oceanographic Inst.Woods HoleUSA
  3. 3.Hawai`i Institute of Geophysics and Planetology, School of Ocean Earth Science and TechnologyUniversity of Hawai`iHonoluluUSA
  4. 4.Department of GeologyUniversity of FloridaGainesvilleUSA

Personalised recommendations