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<p>The impact of the northward subduction of the Meso-Tethys Ocean (Bangong-Nujiang Tethyan Ocean) on the tectonic-sedimentary evolution of the South Qiangtang terrane remains poorly constrained. In particular, the lack of systematic studies on sedimentary records within this subduction system has hindered a deeper understanding of the oceanic basin evolution and the oceanic-continental subduction processes. Here, we present an integrated investigation of sedimentology, petrography, zircon Rare Earth Elements geochemistry, and detrital zircon U-Pb geochronology for the Sewa Formation in the Rialuma section along the southern margin of the South Qiangtang terrane and systematically reveal the depositional environment, provenance characteristics, and tectonic setting of the Sewa Formation. Results indicate that the maximum depositional age of the Lower-Middle Jurassic Sewa Formation is constrained to the Early Jurassic (∼177 Ma). Its lower member consists of barrier island-lagoon deposits, while its upper member is dominated by open-shelf deposits. By comparing detrital zircon U-Pb age spectra and performing multi-dimensional scaling analysis with data from Lower Jurassic clastic rocks along the southern margin of Laurasia, we identify the primary sediment sources. These include the South and North Qiangtang terranes, the Longmu Co-Shuanghu Suture Zone (an accretionary complex), and the Amdo microcontinent. Using the Eu anomaly in detrital zircons, we reconstruct the crustal thickness evolution of the South Qiangtang terrane from 260 to 170 Ma. Further, the <i>r</i><sub>Dz</sub> index indicates that the Early Jurassic Sewa Formation was deposited in a continent-continent collision tectonic setting. Synthesizing these new data with previous studies on the Sewa Formation, we propose that the study area was situated in a back-arc basin during the Early Jurassic, with collision and amalgamation occurring between the Amdo microcontinent and South Qiangtang terrane. These findings provide new sedimentary evidence for the Early Jurassic tectonic evolution of the eastern segment of the Meso-Tethys Ocean.</p>

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Early Jurassic back-arc basin development in the South Qiangtang terrane, Tibetan Plateau: A sedimentary response to the northward subduction of the Meso-Tethys Ocean

  • 期刊论文

  • 发表日期：

    2026年7月16日

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  • Yanshen Liu,
  • Zhongjie Xu,
  • Chaoming Xie,
  • Shiyao Gao,
  • Dazhi Xu

摘要

The impact of the northward subduction of the Meso-Tethys Ocean (Bangong-Nujiang Tethyan Ocean) on the tectonic-sedimentary evolution of the South Qiangtang terrane remains poorly constrained. In particular, the lack of systematic studies on sedimentary records within this subduction system has hindered a deeper understanding of the oceanic basin evolution and the oceanic-continental subduction processes. Here, we present an integrated investigation of sedimentology, petrography, zircon Rare Earth Elements geochemistry, and detrital zircon U-Pb geochronology for the Sewa Formation in the Rialuma section along the southern margin of the South Qiangtang terrane and systematically reveal the depositional environment, provenance characteristics, and tectonic setting of the Sewa Formation. Results indicate that the maximum depositional age of the Lower-Middle Jurassic Sewa Formation is constrained to the Early Jurassic (∼177 Ma). Its lower member consists of barrier island-lagoon deposits, while its upper member is dominated by open-shelf deposits. By comparing detrital zircon U-Pb age spectra and performing multi-dimensional scaling analysis with data from Lower Jurassic clastic rocks along the southern margin of Laurasia, we identify the primary sediment sources. These include the South and North Qiangtang terranes, the Longmu Co-Shuanghu Suture Zone (an accretionary complex), and the Amdo microcontinent. Using the Eu anomaly in detrital zircons, we reconstruct the crustal thickness evolution of the South Qiangtang terrane from 260 to 170 Ma. Further, the rDz index indicates that the Early Jurassic Sewa Formation was deposited in a continent-continent collision tectonic setting. Synthesizing these new data with previous studies on the Sewa Formation, we propose that the study area was situated in a back-arc basin during the Early Jurassic, with collision and amalgamation occurring between the Amdo microcontinent and South Qiangtang terrane. These findings provide new sedimentary evidence for the Early Jurassic tectonic evolution of the eastern segment of the Meso-Tethys Ocean.