Abstract:

          The authors got a  series of  zircon U-Pb ages  for 3  samples  in Dongchuan area, Yunnan province:  the diabase
(TW1) cutting Yinming Formation,  the  ignimbrite  (TW2) of Sahaiguo Formation, and  the sedimentary conglomerate  (TW3) of
Pingdingshan Formation. The SHRIMP zircon U-Pb dating for TW1 yielded an upper intersection age of (1667±13) Ma, which
indicates  the  timing of diabase  intrusion activity  in Mesoproterozoic. The SHRIMP zircon U-Pb dating  for TW2 showed  two
ages: an everage weighted age of （2285±11） Ma can be considered as  the eruption  timing of  lava  in Paleoproterozoic, and  the
upper intersection age of (2742±48) Ma indicates that a series of older rocks might exist in the Dongchuan area. The LA-ICP-
MS dating  for sample TW3 yielded an youngest concordant age of  (1838±10) Ma, which constrained  the oldest sedimentation
age of the Pingdingshan Formation. Based on these dating results, the Precambrian stratigraphic sequence fitting the Dongchuan
area from the older rocks upwards is as follows: Sahaiguo Formation, Wangchang Formation, Caiyuanwan Formation, Pingdishan
Formation, Yinming Foramation, Luoxue Formation, Heisan Formation, Qinglongsan Formation and Dayingpang Formation.

Key words: Dongchuan area, Zircon U-Pb dating, stratigraphic sequence, Precambrian