Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Inconsistent correlation of seismic layer 2a and lava layer thickness in oceanic crust

Abstract

At mid-ocean ridges with fast to intermediate spreading rates, the upper section of oceanic crust is composed of lavas overlying a sheeted dyke complex. These units are formed by dykes intruding into rocks overlying a magma chamber, with lavas erupting at the ocean floor. Seismic reflection data acquired over young oceanic crust commonly image a reflector known as ‘layer 2A’, which is typically interpreted as defining the geologic boundary between lavas and dykes1,2,3. An alternative hypothesis is that the reflector is associated with an alteration boundary within the lava unit4,5,6. Many studies have used mapped variability in layer 2A thickness to make inferences regarding the geology of the oceanic crust, including volcanic construction, dyke intrusion and faulting7,8,9,10. However, there has been no link between the geologic and seismological structure of oceanic crust except at a few deep drill holes. Here we show that, although the layer 2A reflector is imaged near the top of the sheeted dyke complex at fast-spreading crust located adjacent to the Hess Deep rift, it is imaged significantly above the sheeted dykes section at intermediate-spreading crust located near the Blanco transform fault. Although the lavas and underlying transition zone thicknesses differ by about a factor of two, the shallow seismic structure is remarkably similar at the two locations. This implies that seismic layer 2A cannot be used reliably to map the boundary between lavas and dykes in young oceanic crust. Instead we argue that the seismic layer 2A reflector corresponds to an alteration boundary that can be located either within the lava section or near the top of the sheeted dyke complex of oceanic crust.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Study areas and bathymetry maps.
Figure 2: Geologic cross-sections and layer 2A event picks.
Figure 3: Layer 2A event imaged on seismic reflection data.

Similar content being viewed by others

References

  1. Herron, T. J. Lava flow layer — East Pacific Rise. Geophys. Res. Lett. 9, 17–20 (1982)

    Article  ADS  Google Scholar 

  2. Christeson, G. L., Purdy, G. M. & Fryer, G. J. Structure of young upper crust at the East Pacific Rise near 9°30′N. Geophys. Res. Lett. 19, 1045–1048 (1992)

    Article  ADS  Google Scholar 

  3. Harding, A. J., Kent, G. M. & Orcutt, J. A. A multichannel seismic investigation of upper crustal structure at 9°N on the East Pacific Rise: Implications for crustal accretion. J. Geophys. Res. 98, 13925–13944 (1993)

    Article  Google Scholar 

  4. Rohr, K. M. M., Milkereit, B. & Yorath, C. J. Asymmetric deep crustal structure across the Juan de Fuca Ridge. Geology 16, 533–537 (1988)

    Article  ADS  Google Scholar 

  5. Harding, A. J. et al. Structure of young oceanic crust at 13°N on the East Pacific Rise from expanding spread profiles. J. Geophys. Res. 94, 12163–12196 (1989)

    Article  ADS  Google Scholar 

  6. Vera, E. E. et al. The structure of 0- to 0.2-m.y.-old oceanic crust at 9°N on the East Pacific Rise from expanded spread profiles. J. Geophys. Res. 95, 15529–15556 (1990)

    Article  ADS  Google Scholar 

  7. Hooft, E. E. E., Schouten, H. & Detrick, R. S. Constraining crustal emplacement processes from the variation in seismic Layer 2A thickness at the East Pacific Rise. Earth Planet. Sci. Lett. 142, 289–309 (1996)

    Article  ADS  CAS  Google Scholar 

  8. Buck, W. R., Carbotte, S. M. & Mutter, C. Controls on extrusion at mid-ocean ridges. Geology 25, 935–938 (1997)

    Article  ADS  Google Scholar 

  9. Carbotte, S., Mutter, C., Mutter, J. & Ponce-Correa, G. Influence of magma supply and spreading rate on crustal magma bodies and emplacement of the extrusive layer: Insights from the East Pacific Rise at lat 16°N. Geology 26, 455–458 (1998)

    Article  ADS  CAS  Google Scholar 

  10. Schouten, H., Tivey, M. A., Fornari, D. J. & Cochran, J. R. 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 (1999)

    Article  ADS  CAS  Google Scholar 

  11. Searle, R. & Francheteau, J. Morphology and tectonics of the Galapagos triple junction. Mar. Geophys. Res. 8, 95–129 (1986)

    Google Scholar 

  12. Lonsdale, P. Structural pattern of the Galapagos microplate and evolution of the Galapagos triple junctions. J. Geophys. Res. 93, 13551–13574 (1988)

    Article  ADS  Google Scholar 

  13. Francheteau, J. et al. 1 Ma East Pacific Rise oceanic crust and uppermost mantle exposed by rifting in Hess Deep (equatorial Pacific Ocean). Earth Planet. Sci. Lett. 101, 281–295 (1990)

    Article  ADS  Google Scholar 

  14. Francheteau, J. et al. Dyke complex of the East Pacific Rise exposed in the walls of Hess Deep and the structure of the upper oceanic crust. Earth Planet. Sci. Lett. 111, 109–121 (1992)

    Article  ADS  CAS  Google Scholar 

  15. Karson, J. A. et al. Structure of uppermost fast-spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise. Geochem. Geophys. Geosyst. 3 doi: 10.1029/2001GC000155 (2002)

  16. Delaney, J. R., Johnson, H. P. & Karsten, J. L. The Juan de Fuca Ridge - hot spot - propagating rift system: New tectonic, geochemical, and magnetic data. J. Geophys. Res. 86, 11747–11750 (1981)

    Article  ADS  CAS  Google Scholar 

  17. Juteau, T. et al. A submersible study in the Western Blanco Fracture Zone, N.E. Pacific: Structure and evolution during the last 1.6 Ma. Mar. Geophys. Res. 17, 399–430 (1995)

    Article  Google Scholar 

  18. Tivey, M. A. et al. Direct measurement of magnetic reversal polarity boundaries in a cross-section of oceanic crust. Geophys. Res. Lett. 25, 3631–3634 (1998)

    Article  ADS  Google Scholar 

  19. Karson, J. A., Tivey, M. A. & Delaney, J. R. Internal structure of uppermost oceanic crust along the Western Blanco Transform Scarp: Implications for subaxial accretion and deformation at the Juan de Fuca Ridge. J. Geophys. Res. 107 doi: 10.1029/2000JB000051 (2002)

  20. Christeson, G. L., Purdy, G. M. & Fryer, G. J. Seismic constraints on shallow crustal emplacement processes at the fast-spreading East Pacific Rise. J. Geophys. Res. 99, 17957–17973 (1994)

    Article  ADS  Google Scholar 

  21. Vera, E. E. & Diebold, J. B. Seismic imaging of oceanic layer 2A between 9°30′N and 10°N on the East Pacific Rise from two-ship wide-aperture profiles. J. Geophys. Res. 99, 3031–3041 (1994)

    Article  ADS  Google Scholar 

  22. Canales, J. P. et al. Upper crustal structure and axial topography at intermediate spreading ridges: Seismic constraints from the southern Juan de Fuca Ridge. J. Geophys. Res. 110 doi: 10.1029/2005JB003630 (2005)

  23. Alt, J. C. et al. Hydrothermal alteration of a section of upper oceanic crust in the eastern Equatorial Pacific; a synthesis of results from Site 504 (DSDP legs 69–70, and 83, and ODP legs 111, 137, 140, and 148). Proc. ODP Sci. Res. 148, 417–434 (1996)

    Google Scholar 

  24. Expedition 309 and 312 Scientists. Superfast spreading rate crust 3: a complete in situ section of upper oceanic crust formed at a superfast spreading rate. IODP Prelim. Rep. 312, 45–50 (2006)

    Google Scholar 

  25. Alt, J. C., Honnorez, J., Laverne, C. & Emmermann, R. Hydrothermal alteration of a 1 km section through the upper oceanic crust, Deep Sea Drilling Project Hole 504B: Mineralogy, chemistry, and evolution of seawater-basalt interactions. J. Geophys. Res. 91, 10309–10335 (1986)

    Article  ADS  CAS  Google Scholar 

  26. Gillis, K. M. Controls on hydrothermal alteration in a section of fast-spreading oceanic crust. Earth Planet. Sci. Lett. 134, 473–489 (1995)

    Article  ADS  CAS  Google Scholar 

  27. Kent, G. M. et al. Uniform accretion of oceanic crust south of the Garrett transform at 14°15′S on the East Pacific Rise. J. Geophys. Res. 99, 9097–9116 (1994)

    Article  ADS  Google Scholar 

  28. Toomey, D. R., Purdy, G. M., Solomon, S. C. & Wilcock, W. S. D. The three-dimensional seismic velocity structure of the East Pacific Rise near latitude 9° 30′ N. Nature 347, 639–645 (1990)

    Article  ADS  Google Scholar 

  29. Caress, D. W., Burnett, M. S. & Orcutt, J. A. Tomographic image of the axial low-velocity zone at 12°50′N on the East Pacific Rise. J. Geophys. Res. 97, 9243–9263 (1992)

    Article  ADS  Google Scholar 

  30. Karson, J. A. & Christeson, G. L. in Heterogeneity in the Crust and Upper Mantle: Nature, Scaling and Seismic Properties (eds Goff, J. & Holliger, K.) 99–129 (Kluwer Academic, New York, 2003)

    Book  Google Scholar 

Download references

Acknowledgements

We are grateful to the captain, crew and science parties of cruises EW0305 and EW0410 of the R/V Maurice Ewing for their assistance. We also thank G. Kent for comments on the manuscript. This work was supported by the National Science Foundation. This is a UTIG contribution.

Author Contributions G.L.C. and K.D.M. processed and interpreted the seismic data. All authors contributed equally to the integration of the seismic data and geologic observations.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Gail L. Christeson.

Ethics declarations

Competing interests

Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Methods, Supplementary Figures 1-2 with Legends and Supplementary Tables 1-2. (PDF 410 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Christeson, G., McIntosh, K. & Karson, J. Inconsistent correlation of seismic layer 2a and lava layer thickness in oceanic crust. Nature 445, 418–421 (2007). https://doi.org/10.1038/nature05517

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature05517

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing