Thermochronology of the uplift of the Bayan Har Mountains, Qinghai, China

The results of zircon and apatite fission track dating of samples from the Baoyuze granite in the Bayan Har Mountains show that the uplift in the area progressed through three stages: (1) the stage from the low greenschist facies to starting age of the clock within zircons; (2) the stage from the starting age of the zircon clock to that of the apatite clock; and (3) the stage from the starting age of the apatite clock to the surface (present). In the first stage from 200 to 105.57 Ma BP, ~2 km thick materials were unroofed and samples went up to ~6 km below the surface with an unroofing rate of ~0.02 mm/a. In the second stage, as the apatites had risen to ~6 km from the surface, unroofing of ~3 km thick materials was needed for the starting of the clock and this stage of unroofing continued for 101.53 million years and the rate of unroofing was ~0.03 mm/a. In the third stage, because the apatite had already been uplifted to a depth of ~3 km below the surface, 3 km thick materials needed to be removed; the duration for this unroofing was 4.04 million years and the unroofing rate was ~0.74 mm/a.