Techniques for Choosing Target Points during

When dating Zircon U-Pb ages by SHRIMP, choosing the target points of zircon is very important as they directly affects the reliability and accuracy of the results. Some preliminary work needs to be conducted, including taking photographs of reflected and transmitted light, and performing cathodoluminescence. Images of the first two reflect the development of fractures and inclusions. The cathodoluminescence images provide information on genesis and evolution histories of the host rocks. The techniques of choosing target points were summarized for single genesis zircon, core-mantle type zircon and young age single genesis zircon. The photographs of reflected and transmitted light and cathodoluminescence images were used to study the micro-struction and the genesis of zircon before U-Pb dating. When choosing the target points of zircon, the cathodoluminescence images are used to choose the approximate points with clean surface, no fractures and inclusions. The darker area was chosen for single genesis and low U content zircon with young age from cathodoluminescence images in order to obtain smaller error and higher precision dating data.