Early–Middle Permian paleogeomorphic transformations in the northwestern Upper Yangtze region: Implications for the evolution of the eastern Paleo-Tethys oceans

• Stratigraphic ages of the Chihsia-Maokou formations in the NWSCB defined. • The NWSCB paleogeography extended from NW to NE during the Early-Middle Permian • The East Paleo-Tethys evolutions led to tectono-sedimentary changes of the NWSCB. Understanding how the multi-branches subduction of the Paleo-Tethyan Ocean controlled the intraplate tectono-sedimentary evolution of the South China Block (SCB) is fundamental to comprehending the mechanisms of ocean-continent transformation in cratonic basins and the formation of the Sichuan super-basin. This study investigated the Lower–Middle Permian successions (Liangshan, Chihsia, and Maokou formations) on the northwestern margin of the SCB, a critical area lies at the junction between the Songpan–Garzê and Qinling tectonic domains. These Permian successions are subdivided into four three-order sequences based on an isochronous stratigraphic framework that integrates various analyses of lithofacies, gamma-ray, stable isotopes, and zircon U-Pb ages. Lithofacies associations reveal that Lower-Middle Permian sequences record the sedimentary evolution process from shore–swamp environments to rimmed platforms. The paleogeomorphology pattern transitioned from a northwest lowland and southeast highland in the early Permian to a northeast lowland and southwest highland in the middle Permian, with corresponding development of linear high-energy grain shoals trending to northeast and northwest, respectively. These changes in lithofacies and paleogeography were attributed to the evolution of multiple branches of the Paleo-Tethyan, including the opening of the Garzê–Litang back-arc Ocean, along the western margin of the SCB in the Early Permian, followed by the rapid northward subduction of the Mianlue Ocean stretching along the northern margin of the SCB. Our findings demonstrate the regional cratonic tectono-sedimentary evolution coupled the multi-stage and multi-directional subduction of Paleo-Tethyan oceanic branches enhances our understanding of global deep-time multi-sphere interactions.