Earth Science Frontiers ›› 2022, Vol. 29 ›› Issue (1): 266-284.DOI: 10.13745/j.esf.sf.2021.11.45

• A spacial section on The India-Eurasia Collision and Its Long-Range Effect • Previous Articles     Next Articles

Structural characteristics of the Nima Basin in the Bangong-Nujiang tectonic belt, central Tibet

ZHONG Linglin1(), ZHONG Kanghui1,*(), QIN Qin1, YAN Zhao1, YANG Xiong1, HE Zhiyuan2, ZHANG Hongjie1, PENG Jie1, Johan De GRAVE2, Stijn DEWAELE2, ZHOU Huiwen1,3, HE Xingjie1, HAN Wenwen1,4, GONG Xiaobo1,5, YANG Hairui6, DONG Suiliang1,7, CHANG Yupeng1, LI Kaizhi1, DOU Jie1, LI Lin1, HE Mingfeng1, LIU Yilong1   

  1. 1. College of Earth Sciences and MNR Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation, Chengdu University of Technology, Chengdu 610059, China
    2. Department of Geology, Ghent University, Ghent 9000, Belgium
    3. Hainan Geological Bureau, Haikou 570206, China
    4. The No.280 Institute, China National Nuclear Corporation, Guanghan 618300, China
    5. The 106 Geological Team, Sichuan Bureau of Geology & Mineral Resources, Chengdu 610000, China
    6. Institute of Mineral Resources Research, China Metallurgical Geology Bureau, Beijing 100025, China
    7. Chengdu Center, China Geological Survey, Chengdu 610000, China
  • Received:2021-11-25 Revised:2021-12-08 Online:2022-01-25 Published:2022-02-22
  • Contact: ZHONG Kanghui

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Abstract:

The Neo-Tethyan subduction and subsequent India-Eurasia collision resulted in significant contractional deformation of the continental lithosphere and the uplifting of the Tibetan Plateau. Revealing the formation mechanism and process of giant fracture zone in Tibet is crucial for understanding the propagation of the deformation toward the hinterland of the Eurasian continent. Several continental basins of Cretaceous-Cenozoic age developed along the Bangong-Nujiang suture zone, providing a splendid record of the tectonic-sedimentary evolution of the central Tibet. So far, competing geodynamic models are proposed to explain the structural characteristics and the formation of these basins, including strike-slip faulting, extensional rifting and foreland flexural depression. The key to testing these models includes (1) fully documenting the structural characteristics of the basin basement and sedimentary infills and (2) clarifying the structural evolution of the Nima Basin in a regional tectonic context. With these goals in mind, we conducted large-scale geological mapping and structural analyses on the Nima Basin in the Bangong-Nujiang suture. Together with previous research findings, we discussed the tectonic settings, structural characteristics and structural evolution of the Nima Basin and reached the following conclusions: (1) The basement of the Nima Basin mainly consists of metamorphic rocks and marine sedimentary sequences within the Bangong-Nujiang suture zone formed through “soft” collision, and is fractured, with several E-W striking northerly/southerly dipping reverse faults. (2) The Nima Basin is infilled with upper Cretaceous-Neogene multi-cycle fluvial and lacustrine deposits; the terrigenous sedimentary infills later deformed into asymmetric folds with E-W trending axial planes and locally involved in the reactivated basement faults, while multi-phase contractional deformation propagated from the southern edge toward the basin center. (3) The surface structural pattern of the Nima Basin features “two depressions between three uplifts”, where the terrigenous sediments are mostly sourced from the northern imbricate thrust system and the southern fan-shaped extrusion structure, and, along with clasts derived from the central thrust nappes, accumulate in the two depressions—a northern one at the footwall of the imbricate thrusts and a southern one sandwiched between two reverse faults with opposing polarities. (4) The demise of the Bangong-Nujiang Ocean resulted in regional N-S crustal shortening and syncontractional development of the Nima basin in the suture zone, after which the Neo-Tethyan subduction and subsequent India-Asia continental collision triggered repeated reactivation of the basement faults within the Nima region, which invoked both multi-cycle deposition of molasse sequences and propagative deformation. In short, the Nima Basin is a contractional depression basin superimposed over a “soft-collision” type suture zone.

Key words: Bangong-Nujiang suture, continental basin, Nima Basin, structural characteristics, structural evolution

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