新疆东北部三塘湖盆地卡拉岗组火山岩的形成时代:锆石U-Pb定年

Kalagang Formation is developed widely in the Santanghu basin, northeast Xinjiang. The eruption age of volcanic rocks in this Formation was considered as either Permian or Carboniferous. LA-ICP-MS U-Pb dating was made on the basaltic zircons for three samples, which were collected from drill hole (Ma 17) at different depths. Zircons in the basalt at 1543.1 m yield weighed mean age of 343. 5±2. 4 Ma (n = 11, MSWD = 0. 74). Those at 1954. 3 m show two groups of weighted mean ages, 331. 3±5. 0Ma (n = 6, MSWD = 1.4) and 306. 6±5. 3 Ma (n = 9, MSWD= 4. 5), respectively. Zircons in the sample at 2327. 0 m give weighted mean age of 325. 2±3. 0 Ma (n = 19, MSWD = 2. 2). This study considers the minimum age, 306. 6 Ma, as the eruption age of the volcanic rocks in the Kalagang Formation, suggesting that this volcanic suite was formed in Carboniferous instead of formerly widely-accepted Permian. Zircons at the higher depth of the drill hole are old (early Carboniferous) , Zircons at the lower depth are younger (Late Carboniferous). This may indicate that volcanic rocks in Malang depression developed within different ages, showing a characteristic of multi-stage eruption, old zircons at the higher depth of Kalagang Formation may represent the early magma crystallization. Therefore, Kalagang Formation should be formed at the Late Carboniferous.