HR: 10:20h
AN: GP42A-01    [Abstracts]
TI: Tectonic Rotation of Northeastern Tibetan Plateau: Refined age and Geodynamic Implications
AU: * Dupont-Nivet, G
EM: gdn@geo.uu.nl
AF: Paleomagnetic Laboratory "Fort Hoofddijk"; Faculty of Geosciences; Utrecht University, Budapestlaan 17, Utrecht, 3584 CD Netherlands
AU: Reitsma, M J
EM: M.J.Reitsma@students.uu.nl
AF: Paleomagnetic Laboratory "Fort Hoofddijk"; Faculty of Geosciences; Utrecht University, Budapestlaan 17, Utrecht, 3584 CD Netherlands
AU: Krijgsman, W
EM: Krijgsma@geo.uu.nl
AF: Paleomagnetic Laboratory "Fort Hoofddijk"; Faculty of Geosciences; Utrecht University, Budapestlaan 17, Utrecht, 3584 CD Netherlands
AU: Fang, X
EM: fangxm@lzu.edu.cn
AF: Key Laboratory of Western China's Environment, Ministry of Education of China (MOE) & the College of Resources and Environment, Lanzhou University, Lanzhou, 73000 China
AU: Dai, S
EM: daisher@lzu.edu.cn
AF: Key Laboratory of Western China's Environment, Ministry of Education of China (MOE) & the College of Resources and Environment, Lanzhou University, Lanzhou, 73000 China
AU: Cheng, Y
EM: chengyv@163.com
AF: Key Laboratory of Western China's Environment, Ministry of Education of China (MOE) & the College of Resources and Environment, Lanzhou University, Lanzhou, 73000 China
AB: To understand the timing and distribution of deformation during the Indo-Asia collision since ca. 55Ma, tectonic vertical-axis rotations of crustal fragments can be measured using paleomagnetism. Recent work reveals systematic $\sim$ $25\deg$ clockwise rotations in the Xining-Lanzhou region of the northeastern Tibetan Plateau. These results indicate that important deformation propagated far north of the collision zone early after the initial Indo-Asia collision. When compiled with the existing regional paleomagnetic dataset, they support the occurrence of dextral shear on the eastern margin of the Tibetan plateau. However, the age of this major rotation event is only broadly constrained by previous magnetostratigraphic and palynologic results. To obtain precise age and duration of the rotation, high-resolution magnetostratigraphic sampling has been performed on 2 sections spanning inferred Upper Eocene to Lower Miocene strata in the vicinity of the city of Xining. In addition, 30 paleomagnetic sites (8 samples each) have been collected in red mudstone throughout the sections. Ongoing paleomagnetic treatment reveals straightforward characteristic remanent magnetization (ChRM) held by magnetite. Statistical analysis of ChRM directions of normal and reverse polarities indicates 21.0 $\pm$ $7.3\deg$ clockwise rotation in the lower part of the sections while the upper part remains to be analyzed. Expected correlation to the GPTS will provide precise dating of the rotation event. This critical information will enable putting the rotation into possible geodynamic contexts and select between potential mechanisms responsible for the rotation.
UR: http://www.geo.uu.nl/Research/Paleomagnetism/
DE: 8102 Continental contractional orogenic belts
DE: 8110 Continental tectonics--general (0905)
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting