Letter | Published:

Pathway from subducting slab to surface for melt and fluids beneath Mount Rainier

Nature volume 511, pages 338340 (17 July 2014) | Download Citation


Convergent margin volcanism originates with partial melting, primarily of the upper mantle, into which the subducting slab descends1,2. Melting of this material can occur in one of two ways. The flow induced in the mantle by the slab can result in upwelling and melting through adiabatic decompression1,3. Alternatively, fluids released from the descending slab through dehydration reactions can migrate into the hot mantle wedge, inducing melting by lowering the solidus temperature2,4. The two mechanisms are not mutually exclusive1. In either case, the buoyant melts make their way towards the surface to reside in the crust or to be extruded as lava. Here we use magnetotelluric data collected across the central state of Washington, USA, to image the complete pathway for the fluid–melt phase. By incorporating constraints from a collocated seismic study5 into the magnetotelluric inversion process, we obtain superior constraints on the fluids and melt in a subduction setting. Specifically, we are able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.

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We thank V. Maris, M. Brown, A. Kelbert, and Quantec Geoscience, Inc. for their part in data acquisition. We also thank A. Pommier, D. Lizarralde, A. Malcolm, A. Shaw, H. Marschall and J. P. Canales for critical discussions and input on early versions of the manuscript. Finally, we thank P. van Keken for use of his thermal overlay in the magnetotelluric figure. This work was supported by US National Science Foundation grant EAR08-44041 (Principal Investigator R.L.E.) and US National Science Foundation grant EAR08-43725 (Principal Investigator P.E.W.), both through the Earthscope programme. R.S.M. was supported by a National Defense Science and Engineering Graduate (NDSEG) fellowship.

Author information


  1. Department of Geology and Geophysics, MS#22, Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, Massachusetts 02543, USA

    • R. Shane McGary
    • , Rob L. Evans
    •  & Jimmy Elsenbeck
  2. Energy and Geoscience Institute, University of Utah, 423 Wakara Way, Suite 300, Salt Lake City, Utah 84108, USA

    • Philip E. Wannamaker
  3. Department of Earth Science, University of Bergen, Allegaten 41, 5007 Bergen, Norway

    • Stéphane Rondenay


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R.L.E. and P.E.W. conceived the experiment. R.S.M. participated in data collection and was primarily responsible for the processing and inversion work and analysis. R.L.E. was involved in all aspects of the development of the magnetotelluric models. P.E.W. coordinated and led the data collection, and also performed some of the processing and analysis of the broadband data. J.E. assisted with data reduction and processing. S.R. was involved in the production of the seismic image. All authors contributed to the understanding of the results and editing of the manuscript.

Competing interests

The authors declare no competing financial interests.

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Correspondence to R. Shane McGary.

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