Cretaceous and Cenozoic cooling history of the eastern Qilian Shan,north‐eastern margin of the Tibetan Plateau: evidence from apatite fission‐track analysis

The exhumation history and tectonic evolution of the Qilian Shan at the north‐eastern margin of the Tibetan Plateau has been widely debated. Here, we present apatite fission‐track (AFT) data for 12 Ordovician granodiorite samples along a vertical transect in the eastern Qilian Shan. These thermochronometry data indicate that the eastern Qilian Shan experienced a three‐stage cooling history, including: (i) rapid initial cooling in the late Cretaceous; (ii) a stage of quasi isothermal quiescence from ~ 80 to 24 Ma; and (iii) rapid subsequent cooling beginning in the early Miocene. The inferred cooling rates for the three stages are 6.8 ± 4.9 °C Ma^?1, 0.6 ± 0.2 °C Ma^?1 and 2.7 ± 0.9 °C Ma^?1 respectively (±1 σ). Assuming a geothermal gradient of 25 °C km^?1, the exhumation rates for the three stages are 0.27 ± 0.20 mm a^?1, 0.017 ± 0.007 mm a^?1 and 0.11 ± 0.04 mm a^?1 respectively (±1 σ). We suggest that the late Cretaceous cooling records collision of the Lhasa block with the Eurasian continent and that the Miocene cooling represents uplift/exhumation of the Qilian Shan.