Physics
Scientific paper
Nov 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011e%26psl.311..124j&link_type=abstract
Earth and Planetary Science Letters, Volume 311, Issue 1, p. 124-135.
Physics
3
Snake River Plain/Yellowstone, Seismic Tomography, Pacific Northwest Volcanism, Western U.S. Subduction, Continental Hotspots, Subduction Triggered Volcanism
Scientific paper
The Snake River Plain/Yellowstone (SRP/Y) volcanic province is widely considered a classic example of a plume generated continental hotspot. Here we present new S-wave and P-wave tomographic images that suggest an alternative subduction-related process by which volcanism along the SRP/Y hotspot track results from slab fragmentation, trench retreat, and mantle upwelling at the tip and around the truncated edges of the descending plate. Our seismic images of the upper mantle in the depth range 300-600 km show that the subducted oceanic plate extends locally eastward well into the mantle beneath stable North America. The break-up and along-strike fragmentation of the descending plate is related in both time and space to the onset of flood volcanism and the formation of the SRP/Y hotspot. A sub-horizontal branch of the subducting oceanic plate, orphaned from the descending plate by the northward migration of the Mendocino triple junction, resides in the mantle transition zone (400-600 km) directly beneath the SRP/Y track. Its truncated northern edge is parallel to the northwestern margin of the hotspot track and marks the southern edge of a slab gap. A number of recent numerical and physical tank model studies suggest that a rapidly retreating and severely fragmented downgoing plate drives mantle flow around both the tip and the edges of the descending slab. Our seismic results show that the morphology of the subducting slab is appropriate for generating large-scale poloidal flow (producing flood volcanism) in the upper mantle during the re-initiation phase of slab descent ca 20 Ma and for generating smaller-scale toroidal and poloidal upwellings (producing hotspot volcanism) around both the leading tip and northern edge of the slab as it descends into the deeper upper mantle. Plate reconstructions are consistent with the timing and position of both flood and hotspot volcanism.
Carlson Richard W.
Fouch Matthew J.
James David E.
Roth Jeffrey B.
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