Onset timing of significant unroofing around Qaidam basin, northern Tibet, China: Constraints from ⁴⁰Ar/³⁹Ar and FT thermochronology on granitoids

⁴⁰Ar/³⁹Ar and fission track thermochronological results from two granitoid suites in the mountain ranges along the northern and southern edges of Qaidam basin constrain the timing of a Tertiary denudation event and their tectonic association in northern Tibet. The cooling histories based upon ⁴⁰Ar/ ³⁹Ar and fission track ages suggest a rapid cooling event (7.5-10.7 °C/Ma) during Oligocene-early Miocene time. This cooling event is thought to reflect an increasing denudation rate associated with the rapid uplift and denudation of the North Qaidam and Kunlun Shan mountain ranges. With consideration to the field evidence, sedimentation rate of the Qaidam basin, and the propagation rate along the Altyn Tagh fault, the rapid uplifting and denudation are probably due to crustal thickening associated with Cenozoic propagation of the Altyn Tagh fault in accommodating the collision of India with Asia.