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1 The subduction process between the Bangong Co-Nujiang Tethys Oceanic Basin and the South Qiangtang Block is one of the key issues in the study of the Tethys domain. In order to clarify the evolution process and achieve tectonic constraints, the clastic rock and limestone in the northern margin of the Lhasa block and the southern Qiangtang block were studied in detail through the study of magnetic fabric and zircon U-Pb dating. The results show that the depositional age of the Shamuluo Formation is 131-95 Ma, belonging to the Late Jurassic-Early Cretaceous; the Sowa Formation is earlier (163.5-157.3 Ma), belonging to the Late Jurassic. The detrital provenances of the Shamuluo and Suowa Formations are mainly from the magmatic arc of the Lhasa block and the cyclic orogenic belt of the South Qiangtang block. The fabrics of sandstones in the Shamuluo Formation and some sandstones in the Suowa Formation belong to sedimentary magnetic fabrics related to paleocurrent; the limestone and other sandstones of the Sowa Formation are subject to stress and deformation, and belong to the strain fabric related to the structure. A comprehensive study of detrital zircon U-Pb geochronology, magnetic fabric and petrography shows that the Bangong Co-Nujiang ocean basin is affected by plate fragmentation, and there is a north-south two-way subduction. The southward subduction changes in polarity at 163.5-157.3 Ma and begins the northward subduction. At 145 Ma, the Bangong Co-Nujiang Tethys Ocean closed, but the central remnant of Bangong Co-Nujiang Oceanic Basin continued to subduct until 131-102.9 Ma. [ABSTRACT FROM AUTHOR]