新疆伊宁地块坎苏一带LA-ICP-MS锆石U-Pb年龄新资料及其地层归属

New zircon U-Pb age data from LA-ICP-MS and its stratigraphic attribution in the Kansu area of Yining block,Xinjiang

新疆伊宁地块坎苏一带原划泥盆纪坎苏组(变质)火山岩缺乏时代依据,前人或将其归为长城纪,或归为中—晚泥盆世,或归为晚石炭世,地层名称和区域对比也受此影响使用极混乱。在本区进行1∶5万区域地质调查时,对该套地层进行了层序恢复、原岩恢复,并对火山岩类进行了元素地球化学分析和LA-ICP-MS锆石U-Pb定年。研究认为,该套原划泥盆纪坎苏组(变质)火山岩中浅紫红色粗面岩和灰白色云母化英安岩锆石U-Pb年龄分别为315.6±1.6 Ma和306.6±1.2 Ma,侵入于火山岩中的正长花岗岩锆石U-Pb年龄为298.2±1.5 Ma,限定该套火山岩地质时代为晚石炭世。该套火山岩尽管遭受了较强烈的花岗岩类叠加变质和混染作用,但仍显示出大陆裂谷构造环境信息,总体与区域上的晚石炭世伊什基里克组可对比。据此,将原划泥盆纪坎苏组新厘定为晚石炭世伊什基里克组,为该套火山地层时代归属及区域对比提供了确凿证据。

The original Devonian Kansu Formation(metamorphic) volcanic rocks in the Kansu area of Yining block was lack of chronological evidence,with era attribution belonging to the Precambrian Changcheng Period,the Middle-Late Devonian era,or the Late Carboniferous era,leading to confused stratigraphic names and regional correlation.The sequence restoration and proto-rock restoration,elemental geochemical analysis of volcanic rocks and LA-ICP-MS zircon U-Pb dating were carried out,on the basis of 1∶50000 regional geological survey in this area.The results show that the U-Pb ages of the light purplish trachyte and gray white mica-dacite zircons in the original Devonian Kansu Formation(metamorphic) volcanic rocks are 315.6±1.6 Ma and 306.6±1.2 Ma,respectively,and the U-Pb ages of the syenite zircon intrusions into the volcanic rocks are 298.2±1.5 Ma,which defined the geological age of the volcanic rocks as the Late Carboniferous Epoch.Although the volcanic rocks had been subjected to relatively strong granitoid superposition metamorphism and mixing,it still shows the tectonic environment information of continental rift,which is generally comparable to the Late Carboniferous Ishkirik Formation in the region.In view of this,the original Devonian Kansu Formation is newly determined to be the Late Carboniferous Ishkirik Formation,which provides conclusive evidence for the age attribution and regional correlation of volcanic strata.