K-Ar AND~(40)Ar-~(39)Ar GEOCHONOLOGY OF GRANITE FROM THE ALATAO MOUNTAINS,NORTHWEST XINJIANG, CHINA
新疆阿拉套山花岗岩类的K-Ar和~(40)Ar-~(39)Ar同位素定年

More than ten granite bodies are outcropped along the south slop of the Alatao Mountains, northwest Xinjiang Uygur Autonomous region. This area belongs to the the north branch of the Tianshan fold belt. Granites here occur in batholith stockes and their rock types are of granodiorite to mozogranite. KuAr and 40Ar-39Ar dating were performed for 12 biotite samples from 9 rock bodies.The results show that all bodies were emplaced during Variscan orogeny and that they were formed at three stages. Older granodiorites and monzogranites located in the east part of the region were intruded at 305Ma ago. Many monzogranites and alkaline feldspar granites in the west part of region were intruded at 290 to 300Ma ago.The youngest granites outcropped in the west were intruded at about 270 to 280 Ma ago. Tin and tungsten deposits are associated with the granites intruded the second stage. All rock bodies were emplaced Onto a more high level of crust and cooled quickly. The center of magma activities removed from the esst (or northeast) to the west (southwest) with time.