Early Oligocene Onset of the Qilian Shan Uplift in the Northeastern Tibetan Plateau: Evidence From Magnetostratigraphy and Provenance From the Jiuxi Basin

Abstract The India‐Asia collision generated the high topography of the northeastern Tibetan Plateau; yet the timing of its uplift remains debated. Reconstructing the deformation and uplift history of the Qilian Shan (northeastern margin of plateau) is therefore crucial for understanding the region's growth patterns and tectonic processes of the plateau. The well‐exposed, continuous Cenozoic sedimentary record in this area provides a detailed archive of the evolution of these active orogenic belts. This study presents new magnetostratigraphic data from the Baiyanghe section in the Jiuxi basin to constrain the timing of deformation and growth of the Qilian Shan. Our results date the depositional age of the Baiyanghe formation to ∼30–21.8 Ma (early Oligocene to early Miocene). Integrated stratigraphic analysis, paleocurrent data, and provenance results indicate that the Jiuquan basin likely initiated as a foreland basin and began receiving sediments from the Central Qilian Shan by the early Oligocene (∼30 Ma). Synthesizing these findings with prior research, we propose that the Qilian Shan has undergone three phases of tectonic deformation since the early Oligocene: initial uplift in the early Oligocene, northward propagation in the early Miocene, and intense uplift with outward expansion during the middle to late Miocene. Collectively, these findings elucidate the northward expansion of the Tibetan Plateau since the Oligocene.