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Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge

Nature volume 460, pages 89–93 (2009)Cite this article

Abstract

The oceanic crust extends over two-thirds of the Earth’s solid surface, and is generated along mid-ocean ridges from melts derived from the upwelling mantle1. The upper and middle crust are constructed by dyking and sea-floor eruptions originating from magma accumulated in mid-crustal lenses at the spreading axis2,3,4,5,6, but the style of accretion of the lower oceanic crust is actively debated7. Models based on geological and petrological data from ophiolites propose that the lower oceanic crust is accreted from melt sills intruded at multiple levels between the Moho transition zone (MTZ) and the mid-crustal lens8,9,10,11, consistent with geophysical studies that suggest the presence of melt within the lower crust12,13,14,15,16. However, seismic images of molten sills within the lower crust have been elusive. Until now, only seismic reflections from mid-crustal melt lenses2,17,18 and sills within the MTZ have been described19, suggesting that melt is efficiently transported through the lower crust. Here we report deep crustal seismic reflections off the southern Juan de Fuca ridge that we interpret as originating from a molten sill at present accreting the lower oceanic crust. The sill sits 5–6 km beneath the sea floor and 850–900 m above the MTZ, and is located 1.4–3.2 km off the spreading axis. Our results provide evidence for the existence of low-permeability barriers to melt migration within the lower section of modern oceanic crust forming at intermediate-to-fast spreading rates, as inferred from ophiolite studies9,10.

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Figure 1: Seismic reflection profiles located over a bathymetric map of the Cleft segment of the southern JdFR.
Figure 2: Migrated seismic reflection profiles 40 and 75.
Figure 3: Observed and modelled reflection amplitudes and travel times.
Figure 4: Three-dimensional perspective of crustal structure and sea-floor topography.

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Acknowledgements

This research was supported by the US NSF. We thank the captain, crew and scientific party of RV Maurice Ewing Cruise 0207.

Author Contributions All authors participated in the data acquisition experiment. J.P.C. processed the data, interpreted them, and wrote the paper with contributions from all of the co-authors.

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Authors and Affiliations

  1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA,

    J. Pablo Canales & Robert S. Detrick

  2. Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada,

    Mladen R. Nedimović

  3. Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA ,

    Mladen R. Nedimović & Suzanne M. Carbotte

  4. Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA ,

    Graham M. Kent

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  1. J. Pablo Canales
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Correspondence to J. Pablo Canales.

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Canales, J., Nedimović, M., Kent, G. et al. Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge. Nature 460, 89–93 (2009). https://doi.org/10.1038/nature08095

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