Abstract: A set of schist and marble rocks with a few layers of plagioclase amphibolites are distributed to the north of Bashikaogong，Ahun Tash mountains，and experienced amphibolite facies metamorphism．These plagioclase amphibolites exhibit the features of tholeiite in their major element compositions and REE patterns，indicating their basaltic parent rocks．Four samples of these plagioclase amphibolites were analyzed for Sm-Nd isotopes．An isochron with 1 185±130 Ma was obtained whth INd=0．511 40 and ENd(t)=+5．8±0．6，suggesting that these plagioclase amphibolites were formed at the later Mesopmtemzoic and derived from the depleted mantle．Integrated with 40Ar-39Ar data of metamorphic homblendes with the greatest metamorphic age of612±5．8 Ma．it is further proved that these plagioclase amphibolites were formed during the Precambrian．These geochronological and isotopic new data give us some important information about the Late-Precambrian tectonic framework in the Ahun Tagh Mountains．