Article

Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

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Abstract

Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use seismic data to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. Specifically, we analyse these water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the central Cascadia margin. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting must dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.

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Acknowledgements

This research was funded by the US NSF. We thank the RV M.G. Langseth’s and RV Oceanus’ captains, crews, and technical staffs, and the US Ocean Bottom Seismograph Instrument Pool (OBSIP) managers and technical staff for their efforts, which made possible the success of cruises MGL1211 and OC1206A. We thank K. Wang for his review, which improved the manuscript.

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Affiliations

  1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540, USA

    • J. P. Canales
  2. Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA

    • S. M. Carbotte
    •  & H. Carton
  3. Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H4J1, Canada

    • M. R. Nedimović
  4. Institut de Physique du Globe de Paris, 75252 Paris Cedex 05, France

    • H. Carton

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Contributions

All authors are co-PIs of the project and contributed to interpretation of results and manuscript writing. J.P.C. conducted the OBS wide-angle seismic data analysis, tomography modelling, and water content calculations, and led the manuscript writing with substantial contributions from all co-authors. S.M.C. was the programme inception and planning leader, and the Chief Scientist for RV Langseth Cruise MGL0812. J.P.C. and H.C. were co-Chief Scientists for RV Oceanus Cruise OC1206A.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to J. P. Canales.

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