Earth Science Frontiers ›› 2024, Vol. 31 ›› Issue (4): 297-313.DOI: 10.13745/j.esf.sf.2023.9.40

Previous Articles     Next Articles

Middle Eocene thrusting deformation along the Anninghe fault and its regional tectonic implication: Insight from K-Ar dating of authigenic illite-bearing fault gouge

TONG Kui1,2,3(), LI Zhiwu1,*(), LIU Shugen1,4, I.Tonguç UYSAL5, SHI Zejin1, LI Jinxi1, Andrew TODD3, WU Wenhui1, WANG Zijian6, LIU Shengwu1, LI Ke1, HUA Tian1   

  1. 1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China
    2. Post-Doctoral Research Station of Geological Resource and Geological Engineering, Chengdu University of Technology, Chengdu 610059, China
    3. CSIRO Energy, 26 Dick Perry Avenue, Kensington, WA 6151, Australia
    4. Xihua University, Chengdu 610039, China
    5. School of the Environment, The University of Queensland, Brisbane, QLD 4072, Australia
    6. Exploration and Development Research Institute, PetroChina Southwest Oil and Gasfield Company, Chengdu 610051, China
  • Received:2023-04-17 Revised:2023-08-30 Online:2024-07-25 Published:2024-07-10

Abstract:

Deformation characteristics and timing of the fold-and-thrust belt are the key in verifying the geodynamic end-member models of continental lithosphere of the Tibetan Plateau and its periphery. K-Ar dating of authigenic illite from fault gouge provides an effective means in determining the timing of deformation events in the fold-and-thrust belt. The Xianshuihe-Anninghe-Xiaojiang fault is a large-scale sinistral strike-slip fault system accompanying the collision of the Indo-Eurasian Plates and the lateral extrusion of the Tibetan Plateau. The deformation process of the Xianshuihe-Anninghe-Xiaojiang fault system can provide significant insight into how the far-field stress of the Indo-Eurasian collision is transferred eastward. In this study, we focus on the Mianning-Xichang segment of the Anninghe fault. Based on the structural analyses characterizing fault kinematics, we dated authigenic illite from fault gouge to constrain the timing of deformation events along the Anninghe fault. Structural analyses reveal that the Anninghe fault experienced thrusting deformation under the EW-oriented compression. Detailed study of illite clay mineralogy and K-Ar dating of different grain-size fractions of the fault gouge suggest that the components of high-temperature 2M1 illite relative to those of low-temperature 1M/1Md illite polytype gradually decrease with the decreasing K-Ar ages. These results show that different illite K-Ar ages for different grain sizes are due to the mixing of two illite polytypes, represented by detrital 2M1 and authigenic 1M/1Md end members. Illite Age Analysis reveals that the K-Ar age for authigenic 1M/1Md illite is (42.6±9.4) Ma, suggesting that the thrusting deformation along the Anninghe fault occurred in the middle Eocene. Integrated with previously published tectonic, sedimentology, low-temperature thermochronology and paleomagnetism studies, it is suggested that the fold-and-thrust belt in the hinterland of the Tibetan Plateau and its periphery underwent quasi-contemporaneous tectonic compression deformation during the middle Eocene. The dynamic mechanism of this event may be related to the reactivation of the pre-existing tectonic belt caused by the combination of the hard collision of the Indo-Eurasian Plates and intra-continental subduction of the terranes within the Tibetan Plateau. The mid-Eocene thrusting event along the Anninghe fault suggests that the far-field stress from the early stage of the Indo-Eurasian collision has been transferred to the southeastern margin of the Tibetan Plateau.

Key words: Anninghe fault, fault gouge, authigenic illite, K-Ar dating, middle Eocene

CLC Number: