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Deep Mantle Plumes and Convective Upwelling beneath the
Pacific Ocean
Nicholas Schmerr (Carnegie Institution of Washington), Edward Garnero (Arizona State University), Allen McNamara
(Arizona State University)
The 410 and 660 km discontinuities arise from solid-to-solid phase changes in the mineral olivine, and lateral variations in
temperature and composition incurred by dynamical processes in the mantle produce topography on each boundary. To query
discontinuity structure in the presence of mantle downwellings and upwellings, we use underside reflections of shear waves, a
technique that requires the stacking of hundreds to thousands of seismograms. This method has flourished from the deployment
of global and regional seismic arrays, whose data are freely available from the IRIS DMC. We collected a dataset of over 130,000
broadband seismograms that sample beneath the Pacific Ocean. In our study, we resolve the discontinuities to be relatively flat
beneath most of the Pacific, except under subduction zones and volcanic hotspots. We find the phase boundaries are closer
together beneath the Hawaiian hotspot, and also in a larger region of the south Pacific that is flanked by a number of volcanic
hotspots. This region overlies the southern part of the large-scale low shear velocity province in the lowermost mantle, indicative
of a large plume head or cluster of several plumes originating in the lowermost mantle and impinging upon the south Pacific 660
km discontinuity. This feature may be related to large volume volcanic eruptions, such as the Cretaceous Ontong Java Plateau
flood basalts, which have been proposed to originate in the south Pacific.
References
Schmerr, N., et al. (2010), Deep mantle plumes and convective upwelling beneath the Pacific Ocean, Earth Planet. Sci. Lett., 294, 143-151.
Acknowledgements: NSF Grants EAR-0711401, EAR-0453944, EAR-0510383, EAR-0456356
Topography maps for discontinuity depths and transition zone thickness in our Pacific study region. The depths are plotted relative to average values of 418 km, 656
km, and an average transition zone thickness of 242 km.
II-224 | 2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics