Abstract: Wajilitag structure, about 40km southeast to Bachu county, is located at western Tazhong uplift, Tarim basin. There exists a set of slightly metamorphic unfossiliferous clastic rocks at Wajilitag where a developed basic-ultrabasic complex is outcropped. Although the gab-bro ⁴⁰Ar-³⁹Ar age of 821~837Ma was obtained from this complex in 1999, which was the first dating of Precambrian isotopic age in hinterland of Tarim basin, ages of this complex and its surroundings are still questionable. In order to validate the prev ious results, re-collected gabbro samples are used for ⁴⁰Ar-³⁹Ar dating from it, obtaining its plateau age of 879. 12+1.47Ma, corresponding isochronal age of 881.34t 18.82Ma and reverse isochronal age of 880.351 1.22Ma. These measurements indicate that Wajilitag basic-ultrabasic complex was formed in Precam-brian, belonging to a part of Precambian basement in Tarim basin. This conclusion is also supported by related petrochemical analysis, that is, Tarim basin possesses ancient continental crust basement.The magnetic rocks and Palaeozoic strata in Buchu area (including Wajilitag structure) are possibly basement outcrops. This study could be as a guide for hydrocarbon prospecting in Wajilitag structure.

Key words: Tarim basin, Bachu area, Wajilitag, gabbro, ⁴⁰Ar-³⁹Ar dating, Precambrian