The Yellowstone region of the United States is part of an elongated volcanic track that is commonly regarded as the surface expression of a deep mantle plume. Seismic images of the mantle beneath this region suggest that the volcanism could instead result from hot mantle upwelling around the edge of an ancient fragment of subducted oceanic plate.
David James at the Carnegie Institution of Washington and colleagues used seismic wave data to obtain images of the mantle beneath the western United States. Their measurements reveal a remnant of oceanic plate that has broken off from the currently subducting Juan de Fuca plate. It now lies almost horizontally in the upper mantle transition zone at a depth of 500–600 km. The shape and orientation of the plate fragment shows a remarkable match to that of the surface volcanism associated with the Yellowstone hotspot track.
The researchers argue that the fragment separated from the remainder of the subducting plate around 17 million years ago — coincident with the onset of large-volume volcanism in the Pacific Northwest — allowing hot mantle material to upwell around its edges. Yellowstone's volcanic activity may therefore not require a deep mantle plume.
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Whitchurch, A. Fragmented slab. Nature Geosci 4, 819 (2011). https://doi.org/10.1038/ngeo1343
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DOI: https://doi.org/10.1038/ngeo1343
