HR: 1340h
AN: T43C-1335    [Abstracts]
TI: Crustal Structure of the Tarim Basin and Northern Edge of the Tibetan Plateau
AU: * Zhao, J
EM: zhaojm@263.net
AF: China Seismological Bureau, Institute of Geology, Beijing, 100029 China
AU: Mooney, W D
EM: mooney@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd. MS 977, Menlo Park, CA 94025 United States
AU: Zhang, X
EM: shane@usgs.gov
AF: China Seismological Bureau, Geophysical Exploration Center, Zhengzhou, 450003 China
AU: Li, Z
EM: shane@usgs.gov
AF: Institute of Occupational Disease Protection, for Laboring Hygiene of Hunan Province, Changsha, 410007 China
AU: Jin, Z
EM: shane@usgs.gov
AF: Petroleum University, Changping, Beijing, 100048 China
AU: Okaya, N
EM: nihal@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd. MS 977, Menlo Park, CA 94025 United States
AB: We have studied the crustal velocity structure of the northeastern margin of the Tibetan plateau in northwest China using seismic wide-angle reflection/refraction data. The 1200-km-long profile starts at the northern margin of the Tarim basin, crosses the eastern Tarim basin, Altyn Tagh Range and Qaidam basin and ends at the eastern margin of the Qaidam basin. The crust beneath the sedimentary fill of the Tarim basin shows a typical platform/shield crust with an upper (6.1 km/s), middle (6.6 km/s), and lower crust (7.25 km/s) composed of felsic, intermediate and mafic rocks, respectively. In contrast, the crustal velocity structure beneath the Altyn Tagh Range and Qaidam basin suggests that high-velocity ($>$6.9 km/s) mafic lower-crustal material is missing. The Altyn Tagh crust consists of a felsic upper (6.2 km/s), intermediate middle (6.4 km/s), and intermediate-to-mafic lower crust (6.75 km/s); and the Qaidam crust has a felsic upper (6.2 km/s), intermediate middle (6.4 km/s) and lower crust (6.6 km/s). Along the profile, crustal thickness smoothly increases with a thickness of $\sim$50 km beneath the Tarim basin, $\sim$55 km beneath the Atyn Tagh Range and $\sim$60 km beneath the Qaidam basin. The Altyn Tagh crust is underlain by a wedge-shaped area with velocities of $\sim$7.7 km/s which may indicate a crust-mantle mix (i.e. mafic to ultramafic composition). The wedge reaches down to a maximum depth of 90 km below the East Altyn Tagh strike-slip fault suggesting intracontinental subduction of the Tarim mantle (with some involvement of lower Tarim crust) beneath the Altyn Tagh Range.
DE: 8110 Continental tectonics--general (0905)
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7205 Continental crust (1242)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting