月球较地球和球粒陨石亏损挥发性元素，比如月球K/U比值是地球的1/5。该观察事实被认为是月球起源大碰撞高温过程中挥发性元素丢失导致。高温气化-低温冷凝过程中的K同位素分馏已经得到实验证实，因此，地球-月球是否存在全球尺度的K同位素分馏是验证地-月大碰撞气化过程的重要途径，也是制约大碰撞理论物理化学条件的重要因素。根据以上论述，本研究项目拟通过MC-ICP-MS对中国即将采样返回的嫦娥5号样品（2017年）、月球陨石、地幔橄榄岩包体和花岗岩样品进行K同位素研究。通过典型月球样品（月海玄武岩、角砾岩、KREEP岩、斜长岩等）和地球样品（橄榄岩包体和花岗岩）评估地-月全球尺度K同位素差异，示踪地-月大碰撞高温过程。

The moon is depleted in volatile elements, compared with the Earth and chondrite. For example, K/U of the moon is 1/5 of that of the Earth. This observation is long thought to be the result of volatile loss during high-energy moon-forming giant impact. Potassium, as a volatile element, is proved to generate isotopic fractionation in evaporation and condensation. So the whole-sphere K isotopic variation between the Earth and moon is not only a key factor to check the high-temperature evaporation and condensation after that, but also a constraint to the physical and chemical parameters of giant impact. Based on the theory above, we plan to analyze the K isotopes of representative samples of the moon and the Earth, including CE-5 samples (obtained in 2017), lunar meteorites, mantle xenoliths and granites. The K isotopic composition of the Earth and moon would be evaluated by these data, which would be a tracer of the Earth-moon giant impact.