HR: 0800h
AN: T41A-1290    [Abstracts]
TI: Evidence for Triassic sinistral shear along the Altyn Tagh fault, northern Tibet (China)
AU: * Li, H
EM: lihaibing@ccsd.org.cn
AF: Haibing Li Jingsui Yang Cailai Wu Zhiqin Xu, Key Laboratory for Contiental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Yang, J
EM: yangjsui@ccsd.cn
AF: Haibing Li Jingsui Yang Cailai Wu Zhiqin Xu, Key Laboratory for Contiental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Wu, C
EM: wucailai@ccsd.cn
AF: Haibing Li Jingsui Yang Cailai Wu Zhiqin Xu, Key Laboratory for Contiental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Xu, Z
EM: xuzhiqin@ccsd.cn
AF: Haibing Li Jingsui Yang Cailai Wu Zhiqin Xu, Key Laboratory for Contiental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037 China
AU: Tapponnier, P
EM: tappon@ipgp.jussieu.fr
AF: Paul Tapponnier, Laboratoire de Tectonique, Institut de Physique du Globe de Paris, 4 Place Jussieu, 75252 Paris Cedex 05, France., Paris, 75252 France
AU: Arnaud, N
EM: Nicolas.Arnaud@dstu.univ-montp2.fr
AF: Nicolas Arnaud, Universite Montpellier II and UMR 5573, Centre National de la Recherche Scientifique (CNRS), Montpellier France., Montpellier, 34095 France
AB: The strike-slip faults of north Tibet accommodate part of the Cenozoic convergence between India and Asia. Along the Xorkol basin west-north of Qaidam, the active traces of the Altyn Tagh fault follow narrow belts of granitic and amphibolitic mylonites. The deformation recorded in those mylonites is sinistral strike-slip. Three types of zircon may be sorted out from the mylonites: anatectic (magmatic), long columnar zircons, magmatic columnar zircons, and residual, metamorphic, sub-rounded zircon. Three groups of U-Pb ages measured by ion microprobe (SHRIMP) on single zircon were obtained: 530-550Ma for the columnar, magmatic zircon, 460-510Ma for the sub-rounded, residual metamorphic zircon, and 235-245Ma for the long-columnar anatectic (magmatic) zircon. The latter type of zircon is well oriented with the crystal long axis parallel to the stretching lineation. Mineral inclusions in the oriented zircons are also parallel to the stretching lineation, which coincides with the direction of maximum tectonic stress in the process of the strike-slip. Raman spectrum study indicates that the inclusion minerals show the melting phase feature, and cathodoluminescence images show that this type of zircon has a relatively homogeneous internal structure. Therefore, the long columnar zircons resulted from rapid oriented growth in a partial melting regime in the ductile shear process. It not only denotes the direction of shear strain in the strike-slip shear, but the growth age (crystallization age) of this type of zircon denotes the age of strike-slip shear. 40Ar/39Ar ages of directionaly grown hornblendes and biotite in the same samples are 220-230Ma and 190-200Ma, respectively. This suggest syntectonic anatexis and cooling occurred during strike-slip shear along the Altyn Tagh fault in Triassic time (to Early Jurassic). The Triassic shear may be related to oblique collision between the Bayan Har and the Kunlun- Qaidam blocks. 120Ma (Arnaud, et al., 2003) and 90Ma (Liu, et al., 2001) of 40Ar/39Ar ages of deformation from syntectonic fabrics formed in the Karakax segment and central-eastern segment of the Altyn Tagh fault, respectively. The volcanic eruption occurred in early Cretaceous in the eastern end of the Altyn Tagh fault, simultaneity. The Altyn Tagh (Xorkol) shear zone may have formed a unique, continuous boundary in the Triassic, which was later reactivated and sinistral sheared during Cretaceous, and finally reused by the Tertiary strike-slip fault, leading to potentially calculable offsets along the Altyn Tagh fault.
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: Fall Meeting 2005