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Slab melting beneath the Cascade Arc driven by dehydration of altered oceanic peridotite

Nature Geoscience volume 8, pages 404–408 (2015)Cite this article

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Abstract

Water is returned to Earth’s interior at subduction zones. However, the processes and pathways by which water leaves the subducting plate and causes melting beneath volcanic arcs are complex; the source of the water—subducting sediment, altered oceanic crust, or hydrated mantle in the downgoing plate—is debated; and the role of slab temperature is unclear. Here we analyse the hydrogen-isotope and trace-element signature of melt inclusions in ash samples from the Cascade Arc, where young, hot lithosphere subducts. Comparing these data with published analyses, we find that fluids in the Cascade magmas are sourced from deeper parts of the subducting slab—hydrated mantle peridotite in the slab interior—compared with fluids in magmas from the Marianas Arc, where older, colder lithosphere subducts. We use geodynamic modelling to show that, in the hotter subduction zone, the upper crust of the subducting slab rapidly dehydrates at shallow depths. With continued subduction, fluids released from the deeper plate interior migrate into the dehydrated parts, causing those to melt. These melts in turn migrate into the overlying mantle wedge, where they trigger further melting. Our results provide a physical model to explain melting of the subducted plate and mass transfer from the slab to the mantle beneath arcs where relatively young oceanic lithosphere is subducted.

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Figure 1: Cascade Arc regional map and Lassen sample locations.
Figure 2: Melt inclusion compositions and slab surface temperatures.
Figure 3: Hydrogen isotopes: measured values and model results.

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Acknowledgements

We thank A. Kent (Oregon State University) for assistance with the LA-ICP-MS measurements, J. Wang for support in the Carnegie SIMS lab, and T. Plank and J. Lowenstern for helpful discussions. Financial support was provided by the National Science Foundation (grants EAR-1119224 and EAR-1019848) and the Carnegie Institution of Washington.

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Authors and Affiliations

  1. Department of Geological Science, 1272 University of Oregon, Eugene, Oregon 97403, USA

    K. J. Walowski & P. J. Wallace

  2. Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington DC 20015, USA

    E. H. Hauri

  3. Tohoku University, IRIDeS, 6-6-4 Aoba, Aramaki, Sendai, Miyago 980-8578, Japan

    I. Wada

  4. United States Geological Survey, Volcano Science Center, 345 Middlefield Road, MS 910, Menlo Park, California 94025, USA

    M. A. Clynne

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  1. K. J. Walowski
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Contributions

M.A.C., K.J.W. and P.J.W. collected samples, K.J.W. and E.H.H. acquired the geochemical data, I.W. carried out the thermal model calculations. I.W. and K.J.W. performed the fractionation model calculations. All authors participated in writing, revision and interpretation of the data for the manuscript.

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Correspondence to K. J. Walowski.

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Walowski, K., Wallace, P., Hauri, E. et al. Slab melting beneath the Cascade Arc driven by dehydration of altered oceanic peridotite. Nature Geosci 8, 404–408 (2015). https://doi.org/10.1038/ngeo2417

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