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Two phases of shortening across northeastern Tibet as a result of a strong Qaidam lithosphere during the Cenozoic India-Asia collision
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  • Renxian Xie,
  • Lin Chen,
  • An Yin,
  • Xiong Xiong,
  • Yongshun John Chen,
  • Zhen Guo,
  • Kai Wang
Renxian Xie
Southern University of Science and Technology, Southern University of Science and Technology

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Lin Chen
Institute of Geology and Geophysics, Institute of Geology and Geophysics
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An Yin
University of California´╝îLos Angeles, University of California´╝îLos Angeles
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Xiong Xiong
China University of Geosciences, China University of Geosciences
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Yongshun John Chen
Southern University of Science and Technology, Southern University of Science and Technology
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Zhen Guo
Southern University of Science and Technology, Southern University of Science and Technology
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Kai Wang
Innovation Academy for Precision Measurement Science and Technology, Innovation Academy for Precision Measurement Science and Technology
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Abstract

Current geologic observations support two contrasting views on the evolution of the northeastern Tibet north of the Qaidam basin: (1) crustal shortening started at the onset of the India-Asia collision about 50-60 Ma, and (2) crustal shortening did not start until after 20-15 Ma. To reconcile these two seemingly contradicting views supported both by observations, we perform a series of 2-D thermo-mechanical simulations with the goal of assessing the role of the lithospheric structure and strength of the Qaidam basin in controlling the Tibet deformation history. Our simulations yield three end-member scenarios for the first-order Tibetan lithospheric deformaiton: (1) mantle-lithosphere de-lamination in central Tibet accompanied by a deformation-free northern Tibet margin; (2) northward motion and deformation of southern Tibet accompanied by the southward subduction of the Asian lithosphere below northern Tibet, and (3) northward motion and deformation of southern Tibet accompanied by a deformation-free northern Tibet margin. Due to strong crust-mantle coupling of the Qiadam lithosphere, we suggest that the Tibetan lithospheric deformation is accorded with the third scenario. Our model results also show that the pre-existing weaknesses in northeastern Tibet is activated shortly after the onset of the India-Asia collision. This deformation field stays stable until after the removal of the mantle lithosphere in central Tibet, during which a second wave of northward propagating shortening sweeps across northern Tibet north of the Qaidam basin. This result is consistent with the existing data and reconcile the two end-member views on the tectonic history of the northern Tibet.