SHRIMP U-Pb dating and its stratigraphic significance of tuff zircons from Heishan Formation of Kunyang Group, Dongchuan area, Yunnan Province, China

There have been a lot of interests on the formation age of Kunyang Formation and its stratigraphy for a long time, some of the data obtained are referable while there is still a lack of high quality SHRIMP dating. During this time, Sample D0202 in representative of crystal chips and lithic fragments tuff with great stratigraphic significance was collected from middle to upper Heishan Group with a thickness about 180m in Dongyang Area, Yunnan Province, from which over one hundred zircons were picked out to go through SHRIMP U-Pb dating, at the end, it′s indicated that the weighted average age is (1503±17)Ma. Th/U value of Sample D0202 is over 0.48, and it displays a distinct oscillatory zoning structure, which can be regarded as typical magmatic cause, these all indicate that Heishan Formation is formed during Early Mesoproterozoic. This result can further prove that the formation age of Kunyang Group is over 1500 Ma, thus can be provided as an evidence for ascertaining the age and stratigraphy of Kunyang Group.