Seismic Structure and Origin of Hotspots and Mantle Plumes

Details Seismic Structure and Origin of Hotspots and Mantle Plumes Seismic Structure and Origin of Hotspots and Mantle Plumes

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.t51d..04z&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #T51D-04

Physics

7207 Core And Mantle, 8120 Dynamics Of Lithosphere And Mantle: General, 8121 Dynamics, Convection Currents And Mantle Plumes, 8124 Earth'S Interior: Composition And State (Old 8105), 8180 Tomography

Scientific paper

A new model of whole mantle seismic tomography was developed with a novel approach. A grid parameterization was adopted, instead of blocks and spherical harmonic expansions which were used in most of the global tomographic studies. Ray paths and travel times were computed with an efficient 3-D ray tracing scheme [Zhao et al., 1992]. Moreover, the topography of mantle discontinuities at 410 and 660 km depths and the Moho discontinuity [Flanagan and Shearer, 1998; Mooney et al., 1998] were taken into account in the tomographic inversions. The three discontinuities exhibit lateral depth variations of tens of kilometers, which greatly affects the ray path and travel times, hence their depth changes should be taken into account in the inversions. This new approach was applied to a large data set of ISC travel times (P, PP, PcP, pP) which were reprocessed by Engdahl et al. [1998], resulting in a new model of whole mantle P-wave tomography. For the shallow mantle, this new model contains the general features observed in the previous models: a low-velocity ring around the Pacific Ocean basins and high-velocity anomalies under the old and stable continents in the depth range of 0-400 km. One significant difference from the previous models is that stronger and wider high-velocity anomalies are visible in the transition zone depths under the subduction zone regions, which suggests that most of the slab materials are stagnant for a long time in the transition zone before finally dropping down to the lower mantle. Plume-like slow anomalies are visible under the hotspot regions in most parts of the mantle. The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, which suggests that plumes are not fixed in the mantle but can be deflected by the mantle winds. As a consequence, hotspots are not really fixed but can wander on the Earth's surface, as evidenced by the recent geomagnetic and numeric modeling studies. There is a good correlation between the distribution of slow anomalies at the CMB and that of hotspots on the surface, which suggests that many hotspot plumes may originate from the CMB. However, there may be some small-scaled, weak plumes originating from the transition zone depths. Zhao, D. (2001) Seismic structure and origin of hotspots and mantle plumes, Earth Planet. Sci. Lett., in press.

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