SHRIMP zircon U-Pb age measurement: Sample preparation, measurement, data processing and explanation

SHRIMP zircon U-Pb age measurement involves sample collection, zircon separation, mount preparation, analysis of U-Pb isotope composition and data processing as well as explanation. It is important to avoid cross-contamination of various samples in zircon separation, and all kinds of zircons in a rock sample should be separated out, with special attention paid to the finest grains because of their probable minimum age. Zircons mounted in a mount should report features of the population of a sample. In data processing, original data from SHRIMP should be firstly checked in order to find errors and abnormalities, and they should be amended based on the interpolation method of mathematics. In the calculation of weighted average, the rationality of the weight of a U-Pb age should be judged. Generally, it may be older than actuality if the weighted average of modal ages is used as the age of emplacement or eruption of a magma; therefore, it is more reasonable to use the minimum age of zircons in a sample to confine the emplacement or eruption age of a magma.