Letter | Published:

Mid-ocean-ridge seismicity reveals extreme types of ocean lithosphere

Nature volume 535, pages 276279 (14 July 2016) | Download Citation

Abstract

Along ultraslow-spreading ridges, where oceanic tectonic plates drift very slowly apart, conductive cooling is thought to limit mantle melting1 and melt production has been inferred to be highly discontinuous2,3,4. Along such spreading centres, long ridge sections without any igneous crust alternate with magmatic sections that host massive volcanoes capable of strong earthquakes5. Hence melt supply, lithospheric composition and tectonic structure seem to vary considerably along the axis of the slowest-spreading ridges6. However, owing to the lack of seismic data, the lithospheric structure of ultraslow ridges is poorly constrained. Here we describe the structure and accretion modes of two end-member types of oceanic lithosphere using a detailed seismicity survey along 390 kilometres of ultraslow-spreading ridge axis. We observe that amagmatic sections lack shallow seismicity in the upper 15 kilometres of the lithosphere, but unusually contain earthquakes down to depths of 35 kilometres. This observation implies a cold, thick lithosphere, with an upper aseismic zone that probably reflects substantial serpentinization. We find that regions of magmatic lithosphere thin dramatically under volcanic centres, and infer that the resulting topography of the lithosphere–asthenosphere boundary could allow along-axis melt flow, explaining the uneven crustal production at ultraslow-spreading ridges. The seismicity data indicate that alteration in ocean lithosphere may reach far deeper than previously thought, with important implications towards seafloor deformation and fluid circulation.

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Acknowledgements

This study was enabled by grants SCHL853/1-1 and SCHL853/3-1 of the German Science Foundation to V.S. Instruments were borrowed from the DEPAS pool. We acknowledge the efforts of the crews of RV Polarstern cruises ANT-XXIX/2+8 and ARK-XXIV/3, RV Meteor cruise M101 and RV Marion Dufresne.

Author information

Affiliations

  1. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany

    • Vera Schlindwein
    •  & Florian Schmid

Authors

  1. Search for Vera Schlindwein in:

  2. Search for Florian Schmid in:

Contributions

V.S. planned and conducted the surveys, processed data for site 3 and wrote the paper. F.S. processed data from site 1. Both authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Vera Schlindwein.

Reviewer Information Nature thanks S. M. Carbotte and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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DOI

https://doi.org/10.1038/nature18277

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