HR: 10:35h
AN: GP42A-02    [Abstracts]
TI: Paleomagnetism Indicates Mid-Miocene Clockwise Rotation of the NE Tibetan Plateau
AU: * Yan, M
EM: maoduyan@umich.edu
AF: Department of Geological Sciences, Univeristy Of Michigan, 2534 CC Little Building, 425 E University Ave, Ann Arbor, MI 48109 United States
AU: Van der Voo, R
EM: voo@umich.edu
AF: Department of Geological Sciences, Univeristy Of Michigan, 2534 CC Little Building, 425 E University Ave, Ann Arbor, MI 48109 United States
AU: Fang, X
EM: fangxm@lzu.edu.cn
AF: Institute of Tibetan Plateau Research, CAS, P.O. Box 2871, Beilin North Str., Beijing, 100085 China
AU: Fang, X
EM: fangxm@lzu.edu.cn
AF: State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, CAS, Xi'An, 710075 China
AU: Pares, J M
EM: jmpares@umich.edu
AF: Department of Geological Sciences, Univeristy Of Michigan, 2534 CC Little Building, 425 E University Ave, Ann Arbor, MI 48109 United States
AU: Rea, D K
EM: davidrea@umich.edu
AF: Department of Geological Sciences, Univeristy Of Michigan, 2534 CC Little Building, 425 E University Ave, Ann Arbor, MI 48109 United States
AB: The India-Eurasia collision and subsequent continued convergence during the past 55 million years have produced the Himalayas and the Tibetan Plateau. However, the kinematics as to whether the Plateau deformed as a series of rigid blocks or as a viscous continuum are still being debated. Paleomagnetic studies are useful in determining how the India-Asia convergence is being accommodated. Paleomagnetic declinations of studies in and around the Tibetan Plateau reveal important features such as bending of the Himalayan arc, Cenozoic clockwise rotation of the Indochina block, and rotations at the eastern and western margins of the Tibetan Plateau, but the northeastern Tibetan Plateau remained until now rather unknown territory in terms of its kinematics with respect to surrounding areas. To help understand the deformation history of the NE Tibetan Plateau, we have carried out a magnetostratigraphic study in the typical intramontane molasse basin of Guide in the NE Tibetan Plateau, which is bounded by the sinistral Qilian and Kunlun faults to the north and south, and by the dextral Wenquan and Haiyan faults to the southwest and northeast. The declinations observed in the sedimentary strata in the Guide Basin reveal a clockwise rotation of ca. 30 degrees (+/- 17.5 degrees) during the Middle Miocene, implying that the strike-slip faults were particularly active at times during the interval of 17.5 to 11.5 Ma. This and other paleomagnetic and geologic evidence suggest that the northeastern part of the Tibetan Plateau, north of latitude 30N and east of longitude 95E, has rotated clockwise on average about 21 degrees (+/- 8.5 degrees) during the Middle Miocene. It is noteworthy that the SE and NE Tibetan Plateau areas have rotated clockwise during the Miocene, whereas the southern part of the Plateau has rotated counterclockwise some time after the Mid-Eocene. These results are consistent with the predictions of the rotation patterns in the kinematic model of Avouac and Tapponnier (1993).
DE: 9320 Asia
DE: 9604 Cenozoic
DE: 8102 Continental contractional orogenic belts
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting