Structural framework of the central and northern Tibetan plateau as constrained by geologic investigation from Tangula Pass to the southern Qilian Shan thrust belt

HR: 0800h
AN: T41A-1277 [Abstracts]
TI: Structural framework of the central and northern Tibetan plateau as constrained by geologic investigation from Tangula Pass to the southern Qilian Shan thrust belt
AU: * McRivette, M W
EM: mmcrivet@ucla.edu
AF: m.W. McRivette, Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095 United States
AU: Yin, A
EM: yin@ess.ucla.edu
AF: m.W. McRivette, Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095 United States
AU: Chen, X
EM: xhchen@cags.net.cn
AF: Institute of Geomechanics, Chinese Academy of Geological Sciences, Xueyuan Nan Lu #11, Haidian District, Beijing, 100081 China
AU: Burgess, W P
EM: wburgess@ucla.edu
AF: m.W. McRivette, Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095 United States
AB: A preliminary cross section is constructed across central and northern Tibet based on field mapping, reinterpretation of existing geologic maps, analysis of satellite images, and interpretation of seismic-reflection profiles. Our cross section can be divided into 6 segments from south to north. (1) Between the Tanggula Pass and Wenquan over a distance of 80 km are dominated by south-directed thrusts entirely within Jurassic strata. The thrusts are cut by the younger and active east-dipping Wenquan normal fault system that bounds a 70-km long rift directly south of the Tanggula Pass. (2) The 90-km long Yanshiping section to the north is dominated by three major south-verging folds involving both Jurassic and Triassic strata. The folds are tight at their cores, suggesting that they may have detached along a decollement. (3) Between Tuotuo He in the south and Wudaoliang in the north over a distance ~130 km, contraction is expressed by south-directed thrusts that place Carboniferous-Permian strata over Triassic strata or Cretaceous strata over Tertiary strata. The leading-edge south-directed thrust near Tuotuo He truncates the south-verging Yanshiping fold system and places Carboniferous strata atop Triassic strata. Along this segment we also document for the first time the presence of a well-exposed south-dipping normal fault that places Cretaceous red beds over Triassic flysch sequences. (4) The 80-km long section between Wudaoling and the left-slip Kunlun fault in Xidatan is dominated by WNW-striking, south-directed thrusts and folds. They are aligned in an en echelon pattern and merge with the east-striking Kunlun fault at their western ends. (5) The Eastern Kunlun segment consists of the left-slip Kunlun fault system and the south-directed East Kunlun-Qimen Tagh thrust belt. The active Kunlun fault system consists of two main strands: (a) the well-known Xidatan strata as the main Kunlun fault, and (b) the Yieniugou branch to the north. The Yieniugou strand, documented for the first time by this study, has a prominent morphological expression (i.e., prominent fault scarps, left-lateral offset of gullies, en echelon tension fractures against the fault trace). The Yieniugou fault is linked to the east with the Kunlun fault by a NW-striking thrust, whereas to the west it links with the NW-striking and SW-directed Qimen Tagh thrust belt. (6) The structures over the Qaidam basin is dominated by a major south-directed contraction zone consisting of imbricate and duplex systems in the north and a gentle northward tilting of the basin floor in the hanging wall of the south-directed Eastern Kunlun thrust belt. Our geologic investigations lead to the following conclusions: (A) The Eastern Kunlun-Qimen Tagh thrust belt is part of the broad left-slip Kunlun shear zone that aligns in an en echelon fashion against Kunlun fault system. This thrust belt is dominantly south-directed, with major thrusts moving towards the Kunlun fault. (B) The Qaidam basin has been developed as a piggyback basin in the hanging wall of the Kunlun-Qimen Tagh thrust belt and a foreland basin inn the footwall of the southern Qilian Shan thrust belt. (C) The lack of extensional structures in the Paleocene-Eocene Fenghuo Shan Group adjacent to our observed normal fault suggests that Cretaceous extension may have occurred in the northern Qiangtang terrane.
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8104 Continental margins: convergent
DE: 8106 Continental margins: transform
DE: 8109 Continental tectonics: extensional (0905)
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: Fall Meeting 2005