Ziron U-Pb Dating of Volcanic Rocks from Dahalajunshan Formation in Adengtao Area of Zhaosu County, West Tianshan and its Geological Implications

Dahalajunshan Formation volcanic-sedimentary rocks are widespread in Adengtao area of Zhaosu County, West Tianshan, and there is great disparity in its age identification. The volcanic rocks in the Dahalajunshan Formation of Adengtao area are composed of basalt, andesite, dacite, rhyolite and series of relevantpurple, grey, mauve volcaniclastic rocks. Zircon LA-ICP-MS dating has been used to determine the formation ageofrhyolitic volcanic breccia.The results showthat the age of zircon was(344.4±6.1)Ma. Combining with the CL image features of zircons as well as the geological data, the following conclusionshave been reached:the Dahalajunshan Formation was formed not later than early Carboniferous in Adengtao area, West Tianshan.The findings has accurately constrained the period of volcanic strata inthis area, which provides new chronological evidence for volcanic magmatism and tectonic evolution of West Tianshan.