Cenozoic exhumation and deformation propagation along the northeastern Tibetan Plateau margin: constraints from detrital apatite fission-track thermochronology

The northeastern Tibetan Plateau preserves a complex record of Cenozoic deformation, uplift, and basin development associated with the India-Asia collision. However, the timing and spatial pattern of exhumation along the South Qilian Mountains and northern Qaidam Basin margin remain debated. To investigate the tectonic evolution of this plateau margin, we present new detrital apatite fission-track (AFT) data from eight Cenozoic sandstone samples and one modern river sand sample collected along the southern Qilian Mountains and northern Qaidam Basin. Single-grain AFT ages define six major age populations between ca. 94 and 14 Ma, recording multiple phases of source-region cooling and exhumation from the Late Cretaceous to the Miocene. Older populations (P6-P4; ca. 94–50 Ma) dominate Palaeogene strata and reflect prolonged erosion of relatively stable source terranes along the South Qilian margin. Younger populations (P3-P1; ca. 45–14 Ma) become increasingly abundant in Neogene deposits, indicating accelerated exhumation and enhanced tectonic activity during late Cenozoic deformation. Westward sections contain younger cooling populations earlier than eastern sections, suggesting diachronous deformation and eastward propagation of uplift across the northeastern Tibetan Plateau margin. Confined track lengths, Dpar values, and burial-temperature estimates indicate limited post-depositional annealing, demonstrating that most detrital apatite grains preserve primary cooling signals inherited from their source regions. Integrated thermochronologic evidence suggests that the South Qilian Mountains experienced relatively modest exhumation during the Palaeogene, followed by intensified uplift and crustal shortening during the Oligocene-Miocene. These tectonic changes were accompanied by progressive reorganization of sediment supply along the northern margin of the Qaidam Basin. The results support a model of outward plateau growth characterized by spatially variable deformation, episodic exhumation, and progressive propagation of tectonic uplift along the northeastern Tibetan Plateau margin.