Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.u53a..05z&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #U53A-05
Physics
7270 Tomography (6982, 8180), 8121 Dynamics: Convection Currents, And Mantle Plumes, 8124 Earth'S Interior: Composition And State (1212, 7207, 7208, 8105), 8125 Evolution Of The Earth (0325), 8137 Hotspots, Large Igneous Provinces, And Flood Basalt Volcanism
Scientific paper
Multi-scale (local, regional and global scales) tomographic studies are made to determine the 3-D velocity structure of the deep Earth, particularly for imaging mantle plumes and subducting slabs. Plume-like slow anomalies are clearly visible under the major hotspot regions in most parts of the mantle, in particular, under Hawaii, Iceland, South Pacific and Africa (Zhao, 2001, 2004). The slow anomalies under South Pacific and Africa have lateral extensions of over 1000 km and exist in the entire mantle, representing two superplumes. The Pacific superplume has a larger spatial extent and stronger slow anomalies than that of the Africa superplume. The Hawaiian plume is not part of the Pacific superplume (Zhao, 2004). The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, suggesting that plumes are not fixed in the mantle but can be deflected by the mantle flow. Strong mantle plumes under significant hotspots may originate from the CMB. However, there are some small-scaled, weak plumes originating from the transition zone or mid mantle depths (Zhao, 2004). Clear images of subducting slabs and magma chambers in the upper mantle wedge beneath active arc volcanoes are obtained, indicating that geodynamic systems associated with arc magmatism and back-arc spreading are related to deep processes, such as convective circulation in the mantle wedge and dehydration reactions of the subducting slab (Zhao et al., 1997; Zhao, 2004). Evidence also shows that arc magma and slab dehydration may also contribute to the generation of various types of earthquakes in subduction zones (Zhao et al., 2000, 2002). Most of the slab materials are stagnant in the mantle transition zone before finally collapsing down to the CMB as a result of large gravitational instability from phase transitions. The active intraplate volcanoes in East Asia continent (such as Changbai and Wudalianchi volcanoes) are not plume-related hotspots, but are a kind of back-arc volcanoes whose formation was closely related to the deep subduction of the Pacific slab and its stagnancy in the mantle transition zone (Zhao, 2004; Zhao et al., 2004; Lei and Zhao, 2005). The active Tengchong volcano in Southwest China is related to the subduction of the Burma microplate. Zhao, D. (2001) Seismic structure and origin of hotspots and mantle plumes. Earth Planet. Sci. Lett. 192, 251-265. Zhao, D. (2004) Global tomographic images of mantle plumes and subducting slabs: insight into deep Earth dynamics. Phys. Earth Planet. Inter. 146, 3-34.
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