Abstract: The Xingxiaxia region is located in the easternmost part of the central Tianshan block in Chinese Tianshan. The Tianshan orogenic belt has recorded numerous micro-continents, oceanic crust and island arc complex accretional orogeny since the Neoproterozic. In order to further understand the basement evolution and later uplift-denudation of the Tianshan orogenic belt, this study uses ⁴⁰Ar/³⁹Ar and apatite fission track methods to analyze the Precambrian basement rocks, Paleozoic and Mesozoic intrusive rocks in the Xingxingxia area. The results of muscovite and biotite ⁴⁰Ar/³⁹Ar experiments of Xingxingxia Precambrian samples are 239.74±1.54 Ma and 266.20±2.77 Ma. The apatite fission track ages of the precambrian basement and later intrusive rocks are range from 92.5 to 70.5 Ma. Combined with previous results, we suggest that the results of biotite ⁴⁰Ar/³⁹Ar experiments, 239.74±1.64 Ma represents the time of ductile shearing in the area, while the results of muscovite ⁴⁰Ar/³⁹Ar experiments, 266.20±2.77 Ma has many explanations. One is that it represents another period of ductile shearing, and the other is just a cooling time. However, at least one period of ductile deformation occurred in the Xingxingxia area during 260~240 Ma, which may represent the post-collision strike-slip in the Tianshan area after the closure of the North Tianshan Ocean. Thermal simulation results of apatite fission track indicate that, a rapid uplift happened in 90 Ma, which may be influenced by the long-distance effect of the Lhasa block collision or the simultaneous Mongolia-Okhotsk orogeny.

Key words: Xingxingxia, Eastern Tianshan, fission track, 40Ar/39Ar thermochronology, uplift-denudation