HR: 1340h
AN: T23C-1539    [Abstracts]
TI: Magnetochronology of the Plio-Pleistocene Sediments and Multi-pulsed Folding and Thrusting in the Northern Qilian Shan, Tibetan Plateau
AU: * CHEN, J
EM: chenjie@ies.ac.cn
AF: State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Dewai Avenue, Beijing, 100029, China
AU: Wyrwoll, K
AF: School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
AU: LU, Y
AF: State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Dewai Avenue, Beijing, 100029, China
AU: Krapez, B
AF: School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
AU: WAN, J
AF: State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Dewai Avenue, Beijing, 100029, China
AU: LIU, J
AF: State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Dewai Avenue, Beijing, 100029, China
AB: Understanding the tectonics of the large-scale crustal shortening and thickening that produced the Tibetan Plateau, and control its continued growth, has been the focus of many studies in recent years. The NE margin of the plateau is actively growing and is related to the northeastward propagation of the lithospheric-scale Altyn Tagh Fault. The easternmost mountains, the Northern Qilian Shan, rise ca. 4000 meters above the Gobi desert exposing Cambrian-Cretaceous sedimentary strata in thrust-bounded slices. The Jiuxi Basin is one of the small foreland basins and borders the Qilian Shan at its NW margin. Towards the south deformation in the Jiuxi basin is accommodated by a NW-SE fold train (the Laojunmiao fold-and-thrust belt (LFTB)) developed during late Cenozoic. Nearly continuous exposure of deformed Plio-Pleistocene sediments reveal the LFTB particularly favorable for determining the geometry, style, timing, and rate of active faulting and folding within the basin. Paleomagnetic investigations of two Plio-Pleistocene terrestrial successions provide detailed magnetostratigraphy for the upper Cenozoic strata in the basin. Results show that the conglomeratic Yumen Formation is time-transgressive with the basal age ranging from ca. 4.0 Ma in the Niugetao section to ca. 3.5 Ma in the Qingcaowan West section ca.14 km to the northwest at the forelimb of the anticline. Northwestward lateral propagation and growth of the LFTB initiated at ca. 3.0 Ma in the Niugetao, and ca.1.2 Ma in the Qingcaowan West with a rate of ca.7.8 km/Ma. The cross section in the Niugetao provides a conservative estimate of shortening rate of 1.2 mm/yr and uplift rate of 1.1 mm/yr since ca. 3 Ma. Detailed mapping of the rotational offlap-onlap geometrical growth strata at the forelimb indicates multi-pulsed folding and thrusting, which suggests that the LFTB developed as a result of northeastward migration and propagation of thrusting and folding of the NE edge of the Tibetan plateau.
DE: 1520 Magnetostratigraphy
DE: 8005 Folds and folding
DE: 8108 Continental tectonics: compressional
DE: 9320 Asia
DE: 9605 Neogene
SC: Tectonophysics [T]
MN: 2007 Fall Meeting