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

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.