Miocene northward expansion of the NE Tibetan Plateau via intracrustal underthrusting: insight from Cenozoic stratigraphy and provenance studies

The India–Eurasia collision and continued convergence caused significant uplift of the Tibetan Plateau and intracontinental deformation. However, how this convergence was accommodated at plateau margins remains debated, with two main models proposed: pure-shear thickening versus intracontinental underthrusting. Each model implies distinct upper-crustal deformation and sediment source-to-sink systems. To investigate the mode of convergence in the northeastern Tibetan Plateau, this study analyzed Oligocene–Miocene strata from sections at the North Qilian Shan foothills. Stratigraphic analysis reveals upward-coarsening sequences, interpreted to reflect a transition from distal alluvial plain or shallow lacustrine to more proximal settings. Detrital zircon U-Pb dating results show a source-to-sink reorganization during the Oligocene–Miocene, with sources shifting from Late Paleozoic strata to Mesozoic strata of the Central-North Qilian Shan. These findings suggest that the Central-North Qilian Shan experienced northward propagation of uplift, resulting in a progressive decrease in the source distance and corresponding source-to-sink reorganization. This evolutionary pattern contrasts with the persistent proximal sedimentation predicted by the pure-shear thickening model. Combined with previously published geophysical observations and estimates of Cenozoic crustal shortening, these results indicate early Cenozoic tectonic reactivation and Miocene intracrustal underthrusting between the Qilian Shan and Hexi Corridor block.