Upper Cretaceous-Paleocene Magnetostratigraphy of the Longmenshan Foreland Basin and Its Implications for the Tectonic Deformation of the Longmenshan Fault Zone

Knowledge of the history of the tectonic deformation of the eastern edge of Tibet is important for understanding the evolution of the entire Tibetan Plateau; however, the corresponding tectonic deformation process remains controversial. We conducted a detailed rock magnetic and magnetostratigraphic study of the Cretaceous Jiaguan and Guankou Formations (the Jinmenguan section) within the Longmenshan foreland basin on the eastern edge of Tibetan Plateau. The high-temperature remanence components separated after thermal demagnetization passed the A-class reversal test, Bootstrap Cartesian coordinate test, and fold test, at the 95% confidence level. The resulting magnetostratigraphy constrains the age range of the Jinmenguan section to 128.0-64.1 Ma, and that of the Jiaguan Formation to 128.0-83.6 Ma. The resulting chronology identifies two phases of rapid sedimentation (128.0-124.1, 68.8-64.1 Ma) that constrain two phases of tectonic uplift in the Longmenshan Fault Zone on the eastern margin of Tibet during the Cretaceous-early Cenozoic. Our findings suggest that the stress field generated by the subduction and closure of the Bangong-Nujiang Ocean had already been transferred to the eastern edge of the Tibet in the Cretaceous (at similar to 128 Ma).