SHRIMP Zircon U-Pb Dating of Mid-Pleistocene Dacite and Discussion of Relative Problems

K-Ar and U series disequilibria methods have been applied to geochronology research of young volcanic rocks in Tengchong, China. Previous K-Ar dating methods yielded ages of 0.013 to 17.84 Ma and isochron ages of 0.13 to 2.9 Ma in this area. The U series disequilibria method was applied mainly to volcanic rocks that erupted over the past 0.23 Ma. These traditional dating methods could not constrain ages of the volcanic rocks because of their limited accuracy. In recent years, a U-Pb dating method using ion microprobe has shown great potential in geochronology of very young geological bodies, and has been performed on the late Mid-Pleistocene geological bodies abroad. Three dacite samples of Mid-Pleistocene ages from Qushi in Tengchong were obtained by SHRIMP in Beijing SHRIMP Center and they are consistent within uncertainties. After discussing the analytical condition of three tests, such as choice of primary ion species and their intensity, collecting time of secondary ions and some other secondary ion extraction conditions, synthetical analysis on secondary ion counts of all three tests were conducted, indicating that Test 3 (T3) yields the most precise zircon U-Pb age of 0.41±0.01 Ma, which is currently the youngest high precise zircon U-Pb age known in China.