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 similar to 80 to 24Ma; and (iii) rapid subsequent cooling beginning in the early Miocene. The inferred cooling rates for the three stages are 6.8 +/- 4.9 degrees CMa(-1), 0.6 +/- 0.2 degrees CMa(-1) and 2.7 +/- 0.9 degrees CMa(-1) respectively (+/- 1 sigma). Assuming a geothermal gradient of 25 degrees Ckm(-1), the exhumation rates for the three stages are 0.27 +/- 0.20mma(-1), 0.017 +/- 0.007mma(-1) and 0.11 +/- 0.04mma(-1) respectively (+/- 1 sigma). 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.