Recent eruptions on the CoAxial segment of the Juan de Fuca Ridge: Implications for mid-ocean ridge accretion processes

R. W. Embley,¹ W. W. Chadwick,² M. R. Perfit,³ M. C. Smith,³ and J. R. Delaney⁴

¹Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Hatfield Marine Science Center, Newport, Oregon 97365
²Cooperative Institute for Marine Resources Studies, Oregon State University, Hatfield Marine Science Center, Newport, Oregon 97365
³Department of Geology, University of Florida, Gainesville, Florida, 32611
⁴School of Oceanography, University of Washington, Seattle, WA 98195

Journal of Geophysical Research, 105(B7), 16,501–16,525 (2000).
Copyright ©2000 by the American Geophysical Union. Further electronic distribution is not allowed.

Abstract

The 1993 seismic swarm and volcanic eruption on the CoAxial segment of the Juan de Fuca Ridge was the first verified mid-ocean ridge accretion event monitored by the National Oceanic and Atmospheric Administration/U. S. Navy Sound Surveillance System (SOSUS). Ambiguity in the location of the initial seismicity resulted in an uncertainty as to whether the dike intruded from the summit and north rift zone of the adjacent Axial Volcano or whether it arose locally within the CoAxial segment. However, analyses of multibeam, side-scan sonar, towed camera, submersible, and geochemical data show that the CoAxial segment is morphologically, structurally, and geochemically distinct from the north rift zone of Axial Volcano. There is no geologic or geochemical evidence that dike injections from Axial Volcano have extended north of 46°18N in the past, whereas the 1993 eruption site is at 46°31N. Furthermore, all seafloor manifestations of the 1993 dike injection lie along the central neovolcanic zone of the CoAxial segment. Analyses of repeat SeaBeam surveys combined with seafloor observations show that two other eruptions of approximately the same volume as the 1993 eruption occurred along the CoAxial segment in the 1981–1991 interval. These three diking events may have relieved decades of accumulated stress over ~35 km or more of this segment. The spatial pattern and hydrothermal history of the 1993 event is consistent with a dike with a significant lateral component of injection.

• Outline of Paper

  1. Introduction
  2. Sources of Data

  2.1. Multibeam Bathymetry
  2.2. Side-Scan Sonar
  2.3. Submersible and Camera Tow Data

  3. The Structural and Volcanological Context of the Central Juan de Fuca Ridge
  4. CoAxial Segment and Its Relation to Axial Volcano
  5. The 1993 Eruption Site ("Flow Site")
  6. The 1982–1991 Lava Flow at the Flow Site
  7. Floc Site
  8. The 1981–1991 Lava Flows at the "Floc Site"
  9. Southern CoAxial Segment and the "Source Site"
  10. Discussion

  10.1. Relationship of T Wave Seismicity to Seafloor Structure and Geologic Observations
  10.2. Implications for Stress Release During Accretion Events on the Mid-Ocean Ridge
  10.3. Implications for Magma Delivery Systems at Intermediate Spreading Rates

  11. Conclusions and Acknowledgments
  References

• Gallery of Figures and Tables
• Entire Text
  

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