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An inverted continental Moho and serpentinization of the forearc mantle

Nature volume 417, pages 536–538 (2002)Cite this article

Abstract

Volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge, resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere1. Asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back-arc region, but the forearc mantle (in the corner of the wedge) is thought to be significantly cooler. Here we explore the structure of the mantle wedge in the southern Cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers. We find very low shear-wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an ‘inverted’ continental Moho, which reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc region2, consistent with thermal and petrological models of the forearc mantle wedge. This serpentinized material is thought to have low strength and may therefore control the down-dip rupture limit of great thrust earthquakes, as well as the nature of large-scale flow in the mantle wedge.

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Figure 1: Relief map of central Cascadia subduction zone.
Figure 2: Comparison of scattered wave inversion results with thermal model.
Figure 3: S-velocity of altered peridotite as a function of degree of serpentinization.

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Acknowledgements

We thank J. Nabelek and co-workers at Oregon State University for collecting the data set, and R. Benson for facilitating access to the IRIS DMC data archive.

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Author notes

  1. S. M. Peacock

    Present address: Department of Geological Sciences, Arizona State University, Tempe, Arizona, 85287-1404, USA

  2. S. Rondenay

    Present address: Department of Geological Sciences, Brown University, Providence, Rhode Island, 02912, USA

Authors and Affiliations

  1. Department of Earth and Ocean Sciences, The University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada

    M. G. Bostock & S. Rondenay

  2. Pacific Geoscience Centre, Geological Survey of Canada, Sidney, British Columbia, V8L 4B2, Canada

    R. D. Hyndman

  3. School of Earth and Ocean Sciences, University of Victoria, British Columbia, V8W 3P6, Canada

    R. D. Hyndman

Authors
  1. M. G. Bostock
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  2. R. D. Hyndman
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  3. S. Rondenay
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  4. S. M. Peacock
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Correspondence to M. G. Bostock.

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Bostock, M., Hyndman, R., Rondenay, S. et al. An inverted continental Moho and serpentinization of the forearc mantle. Nature 417, 536–538 (2002). https://doi.org/10.1038/417536a

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