Implications of the tectonic rotation of the South Qiangtang Massif for the subduction closure of the BangongCo - Nujiang Tethys Ocean – A study of magnetic fabric and zircon U-Pb chronology

Abstract. In the BangongCo-Nujiang Tethys Ocean, the timing of closure and subduction polarity are key issues in the study of the Tethys domain. Detailed magnetic fabrics and zircon U-Pb dating of marine carbonates collected in the South Qiangtang Massif and clastic rocks collected in the Ban-Nu Suture Zone were carried out to constrain their subduction and collapse processes, from the Middle to Late Jurassic-Early Cretaceous. The results show that the Shamuluo Formation in the suture zone is 131–95 Ma in age, which belongs to the Late Jurassic-Early Cretaceous and develops a primitive sedimentary magnetic fabric; Under the tectonic stress, the limestones in the Middle Jurassic Buqu Formation developed the strongly cleaved magnetic fabric. Meanwhile. the sandstones in the Late Jurassic Sowa Formation developed the tensile lineation and initial deformaed magnetic fabrics. Integrated magnetic fabrics, zircon U-Pb chronology and petrographic studies suggest a WE to SW-NE anticlockwise sinistral movement in the South Qiangtang Massif from the Buqu Formation to the early Suowa Formation; In the Late Suowa Formation, it began a clockwise dextral movement. The change in the direction of massif rotation was associated with a change in the subduction polarity of the BangongCo-Nujiang Tethys Ocean. The BangongCo-Nujiang Ocean changed from southward subduction to northward subduction, which began at the Buqu Formation and ended at the late Sowa Formation (163.5–157.3 Ma). Afterwards, it began to close at 145 Ma and ended its subduction after 131–109.9 Ma, achieving complete closure of the central BangongCo - Nujiang Tethys Ocean.