HR: 14:55h
AN: T13E-05    [Abstracts]
TI: Tomographic Inversion of Pn Travel Times in China: Implications for lithosphere thinning and deformation of North China
AU: * Song, X
EM: xsong@uiuc.edu
AF: Dept. of Geology, Univ. of Illinois, 1301 W. Green St. 245 NHB, Urbana, IL 61801 United States
AU: * Song, X
EM: xsong@uiuc.edu
AF: Center for Analysis and Prediction, China Seismological Bureau, Beijing, 100036 China
AU: Liang, C
EM: cliang@memphis.edu
AF: Dept. of Geology, Univ. of Illinois, 1301 W. Green St. 245 NHB, Urbana, IL 61801 United States
AU: Huang, J
EM: hjl@seis.ac.cn
AF: Center for Analysis and Prediction, China Seismological Bureau, Beijing, 100036 China
AB: Seismic Pn waves sample the top of the upper mantle right beneath the Moho, providing an important tool to probe the temperature, composition, and deformation of the mantle lithosphere. We have recently conducted an inversion of Pn travel times in China from a large collection of Chinese and international earthquake bulletins (Liang et al., 2004, in press). The lithosphere mantle Pn velocities of China are characterized by a mosaic of very fast and very slow anomalies, mirroring the heterogeneity of geology at surface. The major basins show distinct Pn anomalies with high Pn velocity for the basins in the west and low Pn velocity for the basins in North China. The Ordos basin is unique: the Pn velocity in the eastern part of the basin is lower than the average, but the Pn velocity for the western part of the basin is higher than the average. A large area of North China shows prominent low Pn velocities beneath the Archean basement. The thinnest crust of the whole China continent is located in the North China basin. The shape of the crustal thickness contours, trending NNE, correlates well with the shape of the NNE trending North China basin and the Songliao basin, with the crust thickening beneath the Daxin'anling and Taihang mountain ranges to the west. The boundary along the Daxin'anling and Taihang mountain ranges between the thicker crust to the west and thinner one to the east roughly follows the major lineament of the Bouguer gravity anomaly. Our observations are consistent with rifting, lithospheric thinning, and mantle upwelling in the region. The Pn anisotropy is consistent with a dextral simple shear in the NNE direction in the lithosphere mantle during the last (and ongoing) major deformation period. The locations of gold ore deposits in North China and oil deposits in North China and Songliao basins correlate remarkably well with low Pn velocities of the region, suggesting the metallogenesis and oil formation of the region may closely related to magma and thermal activity in lithospheric mantle and crust-mantle interaction since Mesozoic and Cenozoic.
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting