HR: 14:40h
AN: T13E-04    [Abstracts]
TI: Tomgraphic Structure of East Asia: Geodynamic implications
AU: * Chen, Y J
EM: johnyc@pku.edu.cn
AF: Peking University, Department of Geophysics School of Earth & Space Sciences, Beijing, 100871 China
AU: Pei, S
AF: Peking University, Department of Geophysics School of Earth & Space Sciences, Beijing, 100871 China
AU: Pei, S
AF: Institute of Tibetan Plateau Research, CAS, Beijing, 100085 China
AU: Zhao, D
AF: Ehime University, Geodynamics Research Center, Matsuyama, 790-8577 Japan
AU: Yin, A
AF: UCLA, Department of Earth and Space Sciences, Los Angeles, 90095 United States
AU: Ning, J
AF: Peking University, Department of Geophysics School of Earth & Space Sciences, Beijing, 100871 China
AU: Chen, X
AF: Peking University, Department of Geophysics School of Earth & Space Sciences, Beijing, 100871 China
AB: P-wave arrival times of both regional and teleseismic earthquakes were inverted to obtain mantle structures of East Asia. Most important findings of this regional tomography are as follows. (1) No fast P-wave velocity anomalies can be related to subducted oceanic slabs beneath the 660-km discontinuity; instead the subducted oceanic slabs become flattened and stagnant in the transition zone. (2) The western end of the flat stagnant slabs is located ~ 1500 km west of the active trench in the western Pacific, which is correlated with the prominent surface topographic break in eastern China, between the Erdos Plateau to the west and the North China plain in the east, along the NNE-trending Taihang Mountain Range (~105­aE). Based on these observations, we suggested that vigorous mantle convection is operating within this horizontally expanded ­ømantle wedge­ñ above both the active subducting slabs in the western Pacific and the stagnant flat slabs beneath much of the North China plain. This horizontally expanded convection was probably resulted from both rapid eastward migration of the western Pacific trench system and the sinking of the Mesozoic and Cenozoic slabs now trapped at the 660-km transition zone. Both the widespread Cenozoic volcanism and associated extensional basins in East Asia could have been the manifestation of this vigorous upper mantle convection. Finally negative thermal anomaly associated with the stagnant slabs above the 660-km discontinuity has not only caused a broad depression of the boundary due to its negative Clapeyron slope but also effectively shielded the asthenosphere and continental lithosphere above from any possible influence of mantle plumes in the lower mantle.
DE: 8110 Continental tectonics--general (0905)
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting