Magnetostratigraphy of the Niubao Formation in the Bangong‐Nujiang Suture Zone: Constraints on the Amount of Crustal Shortening of the Tibetan Plateau Since 60 Ma.

The Early Cenozoic sedimentary archives of Tibet are crucial for elucidating the geodynamic processes related to continental collision, particularly crustal deformation and shortening. However, the lack of a reliable chronostratigraphic framework for the Cenozoic sedimentary basins in central Tibet has hindered a comprehensive understanding of the influence of the continuous India‐Asia convergence process on the tectonic evolution of the Tibetan hinterland. Here, we report new magnetostratigraphic ages and paleomagnetic results for the Niubao Formation exposed in the northern bank of the Siling Co. Positive field tests and microscopic observations suggest that the remanence is primary. We determine that the depositional age of the measured section was between 59.2 and 48.6 Ma. Our results reveal that the paleogeographic location of the Bangong‐Nujiang Suture Zone during the Late Paleocene–Early Eocene was 25.4 ± 2.1°N, thus supporting the model of two‐stage collision between India and Asia. Plain Language Summary: The tectono‐sedimentary evolution of the Cenozoic terrestrial sedimentary basins in the Tibetan Plateau was a long‐term response to Cenozoic continental collision and was critical for both constraining the amount of crustal shortening of the Asian continent and for paleogeographic reconstruction of the plateau. Nonetheless, the ages of the basins are controversial because of the discordance between radiometric dating results and paleontological ages. Siling Co is the geographic boundary between the Lunpola and Nima Basins, and the Niubao Formation is widely exposed on its northeastern margin, providing excellent research materials for studying the paleogeographic evolution of the plateau. Hence, we established a reliable magnetostratigraphic sequence of the Niubao Formation in northwestern Siling Co, combined with U‐Pb chronology, and constrained its age to 59.2–48.6 Ma. Our updated paleomagnetic results indicate that the paleolatitude of the Bangong‐Nujiang Suture Zone was 25.4 ± 2.1°N during the Late Paleocene–Early Eocene. Combined with the published paleomagnetic data from the intra‐oceanic arc, we suggest that the collision between the Asian and Indian continents had at least two stages and that the paleogeographic location of the collision was above 20°N. Key Points: Detrital zircon U‐Pb ages and paleomagnetic polarity patterns indicate that the Niubao Formation was deposited at 59.2–48.6 MaThe Bangong‐Nujiang Suture Zone was located at 25.4 ± 2.1°N during the Paleocene–EoceneThe amount of crustal shortening in the central Tibetan Plateau since 60 Ma is likely to be 780 ± 330 km [ABSTRACT FROM AUTHOR]